In DPP v Finnegan  TASCCA 3 the Tasmanian Court of Criminal Appeal ruled the trial judge was wrong to refuse leave to the prosecution to cross-examine its own witness.
Three men stood trial for assault. The Crown called a witness, Watkins, who had earlier pled guilty to his involvement. Watkins claimed no knowledge of the incident. The Crown sought leave to cross-examine Watkins under s 38(1)(a) and (b) and (c) Evidence Act 2001 (Tas) – a provision identical to s 38 Evidence Act 2008 (Vic).
The trial judge refused the application. His reasons were reproduced in the appeal [at 4]:
“Well I can’t see any unfairness to Mr Watkins. He, in my view, he’s created this situation and it wouldn’t be unfair to him to be cross-examined. But, there are problems of unfairness to each of the three accused. For a start, Mr Watkins is, according to the account in his interview, a person who was criminally concerned in the events in question. And such people have a tendency, or such people often try to shift blame away from themselves and on to other people, including innocent people. So, it may be that any version of events that he did give would not be accurate and that he would be serving purposes of his own in trying to shift blame on to others. One or more of whom might have been innocent. Secondly, … – if I do give leave …– it’s unrealistic to think that it’s possible or likely that Mr Watkins might do anything other than continuing to maintain that he has no memory of the events in question. That being so, the evidence that he is likely to give will be of no value. And the[re]’ll be a risk of prejudice, in that the jury might act on the information or assertions contained in questions, even if they’re instructed not to do so, and told that answers are evidence but questions aren’t. There’s a risk that they’ll assume any assertions in the questions to be the truth, or to possibly be truth. There’s a risk that they might begin speculating, basing their speculation upon things suggested in questions. And there’s a problem there that any version of events asserted in questions, couldn’t be tested by cross-examination if the witness were to continue to maintain that he is so drug affected that he can’t remember anything. So I think it would be a waste of time to grant leave, but more significantly I think, I think it would … involve a risk of unfair prejudice to each of the three accused, and for that reason I refuse leave.”
The Court of Criminal Appeal agreed that the witness was unlikely to change his story in cross-examination. But the Court held that it would have been legitimate for the Crown to put a prior inconsistent statement to the witness and ask him to adopt it, and that it should have been given the opportunity to do so.
Evans [adding to the primary judgment of Tennant J, Crawford CJ agreeing with both]:
7 The evidence established that Mr Watkins had participated in a police interview some six weeks subsequent to the conduct in question and that there was an audio visual recording of it. In it Mr Watkins had said that he and the three accused, which includes the two respondents, all kicked the complainant to the head and punched him to the head, and were all fully involved in assaulting the complainant while he was on the ground. On the evidence before his Honour it was likely that, if cross-examined, Mr Watkins would agree that he was the person in the audio visual recording of the interview, acknowledge that he had pleaded guilty to a charge of assault arising from his participation in the assault that was the subject of the interview, and acknowledge that he had been convicted and sentenced for that crime. It was also likely that Mr Watkins would maintain that he had no recall of the incident and he had no recall of participating in the interview.
8 Evidence to the above effect from Mr Watkins would not have been a waste of time. It was necessary in order to found an application by the prosecution to lead evidence of the audio visual recording of Mr Watkins’ prior inconsistent statements. Had that application been made and succeeded, the recording would have spoken for itself. In that event, there would not have been an out of the ordinary risk that the jury might act on information or assertions contained in questions put in the course of the police interview, even if directed not to do so. In the course of any trial, when witnesses are cross-examined or when a recording of an accused’s police interview is tendered, it is almost inevitable that questions will have been asked, either by counsel or an interviewing police officer, that contain information or assertions. This does not present a problem that cannot be resolved. It is usually dealt with by a direction to the jury that questions are not evidence.
Unlike under the common law, there’s no impropriety in a party calling a witness just to prove a prior inconsistent statement through them: Adam v R (2001) 207 CLR 96. The Court of Criminal Appeal referred to Tasmania v S  TASSC 84, a case with facts similar to Finnegan.
Tennant J concluded [at 50]:
50 In all the circumstances, I am satisfied his Honour erred in the manner I have identified. As a consequence, the State has been denied at least the opportunity to present to the jury evidence which could have had a significant impact on the trial. The evidence clearly had significant probative value. As a consequence, a miscarriage of justice has occurred. I would give the appellant leave to appeal, and allow the appeal. I would also order that the acquittal of the respondents be quashed and that there be a re-trial.