LEVENTHAL, Circuit Judge:
These appellants were convicted of arson and of carrying a dangerous weapon. They seek reversal on the ground that the trial judge erred in compelling the testimony of one Izzard who had been their companion in crime.
[794]*794The prosecution called Izzard to testify at trial, whereupon the trial judge advised the witness of his privilege against self-incrimination, and asked him if he wished to take the stand. The witness responded in the negative. The prosecuting attorney asked that counsel be appointed to advise the witness. Counsel was appointed; he consulted the witness, and reviewed the transcript of the grand jury proceedings at which the witness had already testified, and he advised the witness to claim his privilege.
Thereafter a long colloquy ensued among court and counsel. The prosecutor urged that the witness should be compelled to testify based on his prior waiver of the privilege at the grand jury proceedings. He argued that there could be no prejudice if the witness merely reiterated what he had already said for the record, and that the standard for waiver under the Supreme Court decisions was that there had to be an actual, realistic possibility of harm.
Government counsel also urged that the defendants had no standing to object to the ruling on the claim of privilege of a witness, and that there could be no prejudice to the witness, if the court erroneously compelled the testimony, in view of Murphy v. Waterfront Comm’n, 378 U.S. 52, 84 S.Ct. 1594, 12 L.Ed.2d 678 (1964), and other Supreme Court decisions. In opposition counsel for witness Izzard contended that there was some doubt in Izzard’s mind as to whether he was being charged or under investigation, etc. at the time he testified before the grand jury, and thus he had not waived his privilege there, and that in any event he had not been given immunity and thus could reclaim the privilege at the subsequent proceeding.
The trial judge rejected outright the Government’s contention that the waiver of privilege before the grand jury carried through to a subsequent proceeding, and subscribed to the rule announced in other circuits, even though there was no binding precedent from this court. He concluded, however, that there was no reason not to compel the testimony, since, under his reading of Murphy v. Waterfront Comm’n, swpra, the witness would be protected from its subsequent use against him.1
On appeal Government counsel invoke the doctrine that a party may not appeal because of the court’s alleged error in overruling the claim of privilege of a witness who is not a party.2 We hold that while this doctrine has vitality, it does not bar review of the action complained of here. For convenience we defer development of this ruling upholding [795]*795appellants’ standing to Part B of this opinion, since it will involve consideration of the material presented in Part A.
As to the merits, we hold (in Part A) that the trial judge erred when he required the witness to testify on the ground that the witness was protected against prejudice by virtue of Murphy v. Waterfront Comm’n. We further hold (in Part C) that there was validity in the prosecutor’s contention that the claim of privilege asserted at trial should be overruled in view of the witness’s voluntary testimony before the grand jury, and that the judge erred in rejecting this contention, and accordingly affirm since we see no valid basis for Izzard’s disavowal of his waiver before the grand jury.
A. The trial judge’s ruling compelling the witness to testify was based on an approach beyond his judicial authority.
1. As to the merits, we begin by saying we agree with the assumption of the trial judge that a witness compelled by a judge to testify over a claim of privilege will be protected under the doctrine of Murphy v. Waterfront Comm’n, 378 U.S. 52, 84 S.Ct. 1594 (1964). While the matter is not free from doubt, the thrust of Murphy and other recent Supreme Court decisions serves to protect the witness.
Appellant Murphy had been held in civil contempt for his refusal to answer questions before a state investigating commission. Murphy argued that the immunity conferred by the state immunity statute was not coextensive with his privilege, since the answers might incriminate him under federal law and lead to federal prosecution.3 All the Justices agreed that the threat of prosecution by a coordinate sovereign whittled away at the policy underlying the privilege and concurred in holding, on different doctrinal grounds, that federal officials would not be permitted to use the testimony or initiate prosecution based on the disclosure or its fruits.4
In Murphy the order to testify was preceded by a grant of immunity pursuant to statute. What of a case where there is compulsion by a judge in the absence of an immunity statute, by an order that erroneously overrules the witness’s claim of privilege? We think the witness is protected by the approach and principle underlying Murphy. See [796]*796also Garrity v. New Jersey, 385 U.S. 493, 500, 87 S.Ct. 616, 17 L.Ed.2d 562 (1967); Lawn v. United States, 355 U.S. 339, 78 S.Ct. 311, 2 L.Ed.2d 321 (1958), both the majority opinion of Justice Whittaker (p. 355, 78 S.Ct. 311) and Justice Harlan’s dissent (p. 363, 78 S.Ct. 311); and Adams v. Maryland, 347 U.S. 179, 181, 74 S.Ct. 442 (1954).5 The Wigmore text also expresses the view that such a court ruling protects the witness.6
2. A trial judge cannot reject a witness’s claim of privilege merely on the ground that the ruling cannot hurt the witness because it will establish an immunity from subsequent prosecution.
We are not here concerned with a case where a judge has made a mistake in applying legal rules, like a case where he erroneously rules that a witness has waived his privilege. In the case before us the judge did not purport to deny that the witness had correctly presented a claim of privilege. He merely asserted that the witness would nevertheless be protected, by Murphy, against prosecution based on his testimony.
The ruling was made by an able and conscientious trial judge. We are confident it was made in good faith, and can even discern how the judge may have come to a mis-reading of Murphy. Nevertheless, his ruling was in the nature of a circular, self-fulfilling prophecy that in substance can only be viewed as a grant of immunity. That ruling was outside the scope of judicial authority.
This is an area that has been considered by Congress and where it has acted with care and particularity, limiting the power to grant immunity — in the presence of a valid claim of privilege — to a limited group of federal officials.7 We [797]*797need not consider what would be the legal situation in the absence of such a statute.8 With that statute on the books, the power to grant immunity is plainly outside the judicial province.
This conclusion, once stated, seems obvious. But if authority is also desired, it appears, at least implicitly, in Ullmann v. United States, 350 U.S. 422, 76 S.Ct. 497, 100 L.Ed. 511 (1956). Justice Frankfurter, writing for seven Justices, rejected appellant’s contentions that the federal immunity statute required the court to participate in the decision as to whether immunity should be granted in a particular situation. The Court approved the approach of the district court, in construing the statute to avoid a serious constitutional question as to the role of the judiciary under the doctrine of separation of powers, and found a limited judicial role under the statute, 18 U.S.C. § 3486 (1964).9 See 350 U.S. at 434, 76 S.Ct. at 504:
Since the Court’s duty under § (c) is only to ascertain whether the statutory requirements are complied with by the grand jury, the United States Attorney, and the Attorney General, we have no difficulty in concluding that the district court is confined within the scope of “judicial power.” (Emphasis added)
The lack of judicial authority to grant immunity from prosecution to a witness whose claim of privilege is recognized also appears in opinions of this court. See Earl v. United States, 124 U.S.App.D.C. 77, 80, 361 F.2d 531, 534 (1966), cert. denied, 388 U.S. 921, 87 S.Ct. 2121, 18 L.Ed.2d 1370 (1967);10 In re Bart, [798]*798113 U.S.App.D.C. 54, 304 F.2d 631 (1962) (by implication).
B. Appellants have standing to object to the judge’s usurpation of prerogative.
We do not entertain this appeal merely to review an erroneous ruling on a claim of testimonial privilege. Here there was a usurpation of a prerogative that Congress has withheld from the courts.
We must look to the substance and not the form of the ruling. What appears to be a mere ruling on a claim of privilege is, “in reality and effect,” 11 an action tantamount to exchanging immunity for the witness’s testimony. If the trial court had been ruling that the witness erred in presenting a claim of privilege the question would simply be whether the judge was correct. But by “resolving [the issue] in terms of the Murphy ease,” the trial court agreed that the witness was quite right in raising the claim of privilege, that he would be deprived of protection to which he was entitled if he testified without asserting the claim of privilege. And then the court in effect asserted the authority of the judiciary to compel testimony simply because the witness would be protected in the future by virtue of the court’s compulsion.
The propriety of such an action by a judge raises serious questions concerning the power of courts and the limitations on their proper role in the administration of justice.12 The issue raised by the District Court’s ruling goes to the distribution of power among the three coordinate branches of Government. This is the kind of issue that is so fundamental that appellate courts are constrained to consider and grant extraordinary writs, if necessary, in order to obviate the extra-judicial encroachment.13 The appellate function embraces a correction in the particular case and deterrence against future repetition.14
The need for a stern restraint on judges to stay within the judicial province is a proper basis for extraordinary appellate consideration- — in some cases, as already noted by mandamus; and in the case before us by recognizing a limited exception to a general rule on standing to raise questions.15 In this area [799]*799there is a particular call for undertaking the task of clarification of the law that is part of the “expository and supervisory functions of an appellate court.” See Will v. United States, 389 U.S. 90, 107, 88 S.Ct. 269, 280, 19 L.Ed.2d 308 (1967); Smuck v. Hobson, 132 U.S.App.D.C. 372, 408 F.2d 175, 1969.16 We must not hesitate to exercise this delicate function, provided our action is consistent with the constitutional limitations embodied in the “ease or controversy” clause and rules prescribed by Congress.
Ordinarily a defendant does not have standing to complain of an erroneous ruling on the scope of the privilege of a witness. That principle most recently announced by this court in Long, is not modified by our opinion today.17 But a defendant does have standing, we hold, to complain that his conviction was obtained in a case where the trial judge went outside his judicial province to grant immunity to a witness. We sustain his standing on the basis of the principle recognized in such cases as Barrows v. Jackson, 346 U.S. 249, 73 S.Ct. 1031, 97 L.Ed. 1586 (1953), and Griswold v. Connecticut, 381 U.S. 479, 85 S.Ct. 1678, 14 L.Ed.2d 510 (1965).18 See also, Berger v. New York, 388 U.S. 41, 55, 104, 87 S.Ct. 1873, 18 L.Ed.2d 1040 (1967).
In Barrows v. Jackson, the Supreme Court recognized that the principle disclaiming standing to raise the rights of third persons who were non-parties was subject to important exceptions, stating (346 U.S. at 257, 73 S.Ct. at 1035) :
Under the peculiar circumstances of this case, we believe the reasons which underlie our rule denying standing to raise another’s rights, which is only a rule of practice, are outweighed by the need to protect the fundamental rights which would be denied by permitting * * * the action to be maintained. * * *
In * * * unique situations which have arisen in the past, broad constitutional policy has led the Court to proceed without regard to its usual rule.
On this point Barrows is in good standing.19
In the case before us that principle leads to according standing to present the constitutional issues — focused as they are in the paramount need for adherence to limitations of judicial power— when presented through the only meaningful channel available. Although the “peculiar circumstances” of Barrows are different on the facts, the essential principle is the same. Barrows is not distinguishable simply because the questions presented here could have been [800]*800raised by Izzard had he chosen to risk contempt and appeal from the resulting order. We must focus on realities, not formalities. Cf. Mills v. Alabama, 384 U.S. 214, 217, 86 S.Ct. 1434, 16 L.Ed.2d 484 (1966). The reality is that the self-fulfilling nature of the District Court’s ruling effectively eliminated Izzard from the action below. It would be unrealistic to project that an appeal could or might have been lodged by a witness who was wronged, since the ruling gives him de facto protection and resistance would expose him to possible punishment for contempt, at a minimum, and to the risk of antagonizing the prosecutor.20 As in Barrows the issue on this appeal would likely be effectively foreclosed from review if we do not “proceed without regard to [the] usual rule.”
We repeat that this opinion does not modify the rule of Long for the broad areas of issues, where what is involved is an alleged error on an evidentiary question, or in definition whether the witness properly raised a claim to protection. But in this case, where the trial judge did not disagree with the witness’s claim of right to protection, but proceeded by an action that was tantamount to granting immunity, we conclude that a defendant adversely affected in fact has standing to bring such departure from the judicial province to the appellate court for review and correction.
C. The privilege against self-incrimination cannot be claimed at trial by a witness who has voluntarily testified, before the grand fury which returned the indictment, without invoking the privilege.
In our view a witness who voluntarily testifies before a grand jury without invoking the privilege against self-incrimination, of which he has been advised, waives the privilege and may not thereafter claim it when he is called to testify as a witness at the trial on the indictment returned by the grand jury, where the witness is not the defendant, or under indictment.
While the prevailing rule is that a waiver of Fifth Amendment privilege at one proceeding does not carry through to another proceeding,21 there appears to be no controlling authority in this circuit. We think that rule unsound, at least for the circumstance before us, and decline to adopt it.22
L10] Although numerous policies have been advanced to explain and support the privilege against self-incrimination,23 the paramount interest that is protected is the right to remain silent rather than make disclosures that may in fact lead to prosecution. When prosecution is barred for some reason, no privilege exists. Witnesses are compelled to speak when jeopardy has attached, the statute of limitations has run, a pardon has been granted, or adequate immunity conferred.24 The rationale for these [801]*801holdings is that the witness’s disclosure cannot prejudice him since he is no longer subject to prosecution.
Once a witness has voluntarily spoken out, we do not see how his protected interest is jeopardized by testifying in a subsequent proceeding, provided he is not required to disclose matters of substance which are unknown to the Government. We see “no real danger of legal detriment” arising out of a second disclosure. Compare Rogers v. United States, 340 U.S. 367 at 373, 71 S.Ct. 438, 95 L.Ed. 744. In short we agree with Professor McCormick’s criticism of the prevailing rule:
A mechanical rule has been placed upon the application of [the] doctrine of waiver. * * * Consequently, a witness * * * who freely testifies before the Grand Jury * * * when called as a witness at the trial * * * may claim the privilege. * * * The rule * * * protects chiefly the person accused of crime, and gives very little protection to the witness. If he has already given material evidence of his own guilt, such evidence, in the form of a transcript of his testimony, or of a signed affidavit, can readily be proved against him if he is tried for the crime. The present testimony [i. e. second disclosure] will not add to his hazard except as additional facts or details are brought out.25
The rule we think sound is like the rule put forward in the Restatement and the proposed Uniform Rules of Evidence.26
The community’s interest in law enforcement is a fundamental basic concern of our country, for freedom and security are intertwined. That interest cannot be used to justify trampling on the Constitution. The need for “intelligent and effective law enforcement” is, however, rightly taken into account in defining the scope of constitutional protections.27 Those protections are not to be extended by “mechanical rules” that serve no meaningful freedom, but interfere with and hamper sound law enforcement.
It would impede sound law enforcement if an implicated but cooperating witness can decide, after he has made disclosure to the grand jury, that he will refuse to testify at trial. The Government may have structured its case around this witness, and be unable at a late hour, often after jeopardy has attached, to recast an investigation. Leads that might have been explored in the past, with expenditure of much money and time, and were put aside with this witness’s cooperation, may now be lost beyond retrieval. The witness may have obtained an effective immunity for him[802]*802self, especially if the investigation ripened just before the expiration of the statute of limitations, and then be able to balk all prosecution. And even a cooperative witness may be made vulnerable, by a doctrine that gives him choice, to the threats and blandishments of the defendant. There are doubtless other considerations of like import, but these suffice to establish the interest of law enforcement.
What of the other side of the coin? Is there a Fifth Amendment policy that would be furthered by restricting a witness’s waiver before the grand jury so as to give him a mint-new privilege at trial? We can discern none. As Professor McCormick notes, such restriction “gives very little protection to the witness” once he has already disclosed incriminating facts. Although it has been suggested that the privilege protects a privacy interest,28 reflection makes it clear that this is not the crucial interest, for it does not survive to protect the privilege once the fear of prosecution is gone, as in case of granted immunity.29
We turn to the precedents, to see if they require us to shrink from the reach of reason. Appellants have cited no Supreme Court decisions. To the extent that the Supreme Court’s opinions offer guidance on the question before us, we think that they support a realistic rather than mechanical approach to the application of waiver. While the Court’s decisions manifest extreme concern for safeguarding the privilege against self-incrimination and implementing its policies,30 the Court has consistently refused to uphold refusals to testify when there is no “real” and substantial “hazard of incrimination.” See Marchetti v. United States, 390 U.S. 39, 48, 53, 88 S.Ct. 697, 19 L.Ed.2d 889 (1968); Hoffman v. United States, supra, 341 U.S. at 486, 71 S.Ct. 814. In Rogers v. United States, supra, 340 U.S. 367, 71 S.Ct. 438, cited in Malloy v. Hogan, 378 U.S. 1, 84 S.Ct. 1489 (1964), the Court emphasized that “the privilege against self-incrimination presupposes a real danger of legal detriment arising from the disclosure * * * ” 340 U.S. at 372-373, 71 S.Ct. at 442. Accordingly the Court held that a witness who volunteered incriminating answers to the Grand Jury could not invoke the privilege as to details which “would not further incriminate.” 340 U.S. at 373, 71 S.Ct. at 442. The issue is “whether the question presented a reasonable danger of further crimination in light of all the circumstances, including any previous disclosures, * * * whether the answer * * * would subject the witness to a ‘real danger’ of further crimination.” 340 U.S. at 374, 71 S.Ct. at 442.
The privilege of course remains as to matters that would subject the witness to a “real danger” of further crimination, and that the witness need not demonstrate that danger “in the sense in which a claim is usually * * * demonstrated in court.” Hoffman v. United States, supra, 341 U.S. at 486, 71 S.Ct. at 818. The witness is not required to run the risk if the answers may have a tendency to incriminate. Malloy v. Hogan, supra at 12, 84 S.Ct. 1489.
The Supreme Court has plainly tried to strike a balance between the policy of the privilege and the requirement for information. Generally the balance weighs heavily in favor of the privilege, but the witness’s latitude in invoking his right requires at least an arguable contention of a real danger of legal detriment. Since it is our clear conviction that a finding of waiver in the case before us exposes the witness to no real danger of legal harm, the principles applied by the Supreme Court stand against the privileges claimed at the trial of appellants.
[803]*803Various grounds have been advanced in the cases that refuse to find a waiver. In United States v. Miranti, 253 F.2d 135 (2d Cir. 1958), the court sustained Miranti’s refusal to answer questions before a grand jury investigation even though he had previously testified before a grand jury and been tried and convicted. The court focused on the period that elapsed between the two investigations. It noted that the eases drew a distinction between two appearances in the same proceeding and appearances in different proceedings, saying as to the latter group:
[The] prior disclosures were held not to constitute a waiver in the subsequent proceedings for the reason that during the period between successive proceedings conditions might have changed creating new grounds for apprehension (e. g., the passage of new criminal laws) or that the witness might be subject to different interrogation for different purposes at the subsequent proceeding. 253 F.2d at 140.31
It may be that in some situations the passage of time, and change in purpose of an investigation, may open up new real dangers. The question must be faced realistically, however, and not mechanically. In the case before us involving a grand jury presentation and then a trial without unusual delay, this danger does not have substance.32
In Miranti the court also said that reiteration constituted a danger because
[R]eiteration adds to the credibility of the statement, * * * and if construed as a waiver could lead to additional questions requiring answers which further implicate the witness. 253 F.2d at 139-140.
If reiteration alone is sufficient for realistic new incrimination that would also prohibit a subsequent appearance before the same tribunal, and that plainly is not the law. Rogers v. United States, supra.
There may be a problem if a witness is asked questions that go beyond his previous disclosure. The Miranti court may have been sensitive to this problem because the witness was before a grand jury, which might run rough shod over subtle questions that might arise. Unlike Miranti the case before us involves a second disclosure at trial, in the presence of a judge, and for the same offenses considered by the Grand Jury. Compare United States v. Steffan, supra note 31 (“cases different”).
To the extent that defense counsel’s cross examination might probe matters of substance as yet unrevealed, the witness must retain his privilege, and the Government runs the risk of a mistrial or reversal, since the defendant cannot be deprived of his Sixth Amendment right to confrontation.33 The [804]*804Government is not being exposed to an unreasonable burden, since it can control the scope of cross examination by its presentation on direct.34
But it does assume some risk in presenting a nonrecalcitrant witness if he can successfully assert his privilege in response to probing that lies within the latitude to which a defendant is entitled on cross examination of a witness. A realistic approach to the privilege, and possibility of “real danger,” does present more problems to counsel and courts than a mechanical rule. Simple solutions cannot always be found in a complex society. The call of the law lies, however, in a diligent effort to give just weight to the various interests of individuals and their society, and to harmonize them with maximum attention to reality.
We now turn to In re Neff, 206 F.2d 149 (3d Cir. 1953), for a fuller discussion of the precedent that seems to have launched the doctrine invoked by the witness and the trial judge. Sylvia Neff was convicted of contempt for refusing to answer questions put to her as a subpoenaed witness at the trial of Anthony Valentino. Valentino had been under investigation by the grand jury and the witness Neff had been called to testify during the hearings. Between the grand jury investigation and Valentino’s trial appellant had been convicted for perjury, with her appeal pending before the circuit court. At trial the prosecution sought to put questions that had already been answered before the grand jury. Neff had been in contact with her counsel, and she requested a recess which was denied by the trial judge. The court in discussing the waiver question relied on the “settled” rule that “a person who has waived his privilege of silence in one trial or proceeding is not estopped to assert it as to the same matter in a subsequent trial or proceeding.” 206 F.2d at 152. The only Supreme Court decision cited for the proposition is Arndstein v. McCarthy, 254 U.S. 71, 41 S.Ct. 26, 65 L.Ed. 138 (1920). That case does not, however, speak to the question of waiver. In Arndstein the eontemnor had filed certain schedules during the course of a bankruptcy proceeding. It appears that during the course of the same proceeding appellant was interrogated as to the schedule and set up his privilege. In the Court’s words:
The writ [of habeas corpus seeking release for the contempt conviction] was refused upon the theory that by filing schedules without objection the bankrupt waived his constitutional privilege and could not thereafter refuse to reply when questioned in respect to them. This view of the law we think is erroneous. The schedules alone did not amount to an admission of guilt or furnish clear proof of crime and the mere filing of them did not com stitute a waiver of the right to stop short whenever the bankrupt could fairly claim that to answer might tend to incriminate him. 254 U.S. at 72, 41 S.Ct. at 26. (Emphasis added.)
The holding of Arndstein is consistent with the view later espoused in Rogers, Hoffman and Marchetti. The witness in Arndstein was not asked merely to repeat incriminating statements that he had already made, but was interrogated as to new matter of substance. See Rogers v. United States, supra, 340 U.S. at 374, 71 S.Ct. 438. It is evident that a real danger of legal detriment existed.
Neff relies also on the point that a trial is a separate proceeding from the grand jury investigation and not a mere continuation of the same proceeding. We think, however, that this is a “mechanical limitation” that fails to focus on the underlying interests: whether the witness’s privilege is jeopardized, and the interest of the community in obtaining full disclosure at criminal trials.
[805]*805However sound the result in Neff on its facts,35 we decline to adopt its broad language as controlling for all circumstances. We think the better rule is to hold that the waiver carries through unless there is new material, or possibly new conditions,36 that may give rise to further incrimination. To the extent that the Neff court apprehended prejudice from the mere fact of repetition of the earlier testimony we reject its holding.
We hold that where a non-indicted witness has waived his Fifth Amendment privilege by testifying before a grand jury voluntarily and with knowledge of his privilege, his waiver extends to a subsequent trial based on an indictment returned by the grand jury that heard his testimony. We repeat, for emphasis, that our holding does not apply when the witness is himself accused or under indictment. We also hold that the witness is entitled to counsel, either his own or court appointed, and may object to any question that would require disclosure of new matter of substance.
In our view this approach accommodates both the policies underlying the Fifth Amendment’s privilege and the interest of obtaining full disclosure whenever possible in criminal trials.
D. Disposition of the case before us.
Our disposition is shaped by the scope of appellants’ standing, cf. Smuck v. Hobson, supra, which is limited to the propriety of the trial judge’s granting immunity to Izzard. While we disagree with the theory of the District Court, reversal does not follow since his ruling is sustainable on other grounds, which we have set forth in Part C.
As there noted we hold that a witness’s voluntary testimony before a grand jury is a waiver for purposes of trial. This still leaves room for consideration of whether under the facts of any particular case the witness’s pre-trial statement constitutes a waiver.37
If the trial judge had considered the question and ruled there was a waiver, the defendant would not have standing to attack the ruling, even if [806]*806erroneous, as a ground of reversal. In this case the trial judge did not make a ruling but we feel the record before us is clear enough to indicate that the interest of justice does not justify a remand. The transcript shows (Tr. 42-44) that Izzard expressly stated to the grand jury that he had consulted a lawyer prior to going before the grand jury; that he wished to cooperate with the Government though he understood he did not have to; that this cooperation was voluntary, and that he knew anything he said could be used against him. Izzard’s counsel at trial pointed out that before the grand jury Izzard said he did not think he was presently charged for the offense. We think this of no significance. Izzard subsequently and expressly testified to the grand jury that he did understand, and his attorney had explained that anything he said could be used against him; and understanding that it was his wish to tell what he knew about the case.38
The judgment is
Affirmed.