The late David Ross QC had some excellent advice for a practitioner proofing a witness (taken from his timeless book on the subject; Advocacy):
“Some Bars allow you to see the client and the witnesses, and some not. If you do see them, have someone else present, speak to them one by one, suggest no line and do not say what another witness has told you.”
The Victorian Bar Practice Rules do allow barristers to meet with witnesses, and have this to say [at Rules 44 and 45]:
(a) Under no circumstances shall a barrister advise or suggest to a witness that false evidence should be given.
(b) A barrister shall not coach a witness by advising what answers the witness should give to questions which might be asked.
A barrister will not have breached Rule 44 by expressing a general admonition to tell the truth or by questioning in conference the version of evidence to be given by a prospective witness, including drawing the witness’s attention to inconsistencies or other difficulties with the evidence, but must not coach or encourage the witness to give evidence different from the evidence which the witness believes to be true.
In Majinski v Western Australian  WASCA 10 the appellant sought to impugn the conduct of the prosecutor who spoke to the complainant, a boy, prior to the commencement of a sex assault case.
Martin CJ [at 11]:
A hearing for the pre-recording of the complainant’s cross-examination was scheduled to take place on 2 June 2011. In preparation for that hearing, a prosecutor met with the complainant on 26 May 2011. Following that meeting, the prosecutor wrote to defence counsel by letter dated 26 May 2011. It appears that the letter followed a telephone conversation between counsel.
The letter first deals with proposed editing of the visually-recorded interview of the complainant. The letter then advises that the prosecutor met with the complainant earlier that day, when his visually-recorded interview was played to him. The letter then sets out further information that was given by the complainant to the prosecutor during the course of their meeting. Generally speaking, the information amplified the statements made by the complainant during his earlier recorded interview.
The letter further advised that during the meeting, the complainant created or marked documents depicting the lay-out of the area in which the offences were allegedly committed.
The letter further advised that the complainant was shown a number of photographs which were in the prosecution brief, and identified his response at the time he was shown each photograph. It is clear from that portion of the letter that the complainant was shown a photograph of the appellant, to which he replied ‘that’s him. He did have a tattoo’. There are a number of photographs of the appellant in the prosecution brief which show that he has a relatively full head of dark hair, and a number of tattoos on each arm.
There is nothing in the text of the letter which suggests that the prosecutor suggested or indicated to the complainant the answers that he should give during their meeting. However, following receipt of the letter, counsel acting on behalf of the appellant brought an application for a permanent stay of proceedings on the basis that the complainant had been coached by the prosecutor, with the result that his evidence was irrevocably tainted and suspect.
During the application, the complainant gave evidence and was cross-examined. He testified that at no point during the proofing session did the prosecutor tell him what to say, and that the prosecutor let him answer questions by himself. Further, notwithstanding that the complainant identified the appellant from a photograph which showed tattoos on his arms and depicted him as having a full head of dark hair, the complainant adhered to the statements he had made during his earlier interview with police to the effect that the offender was balding and had no tattoos. While the judge was critical of the conduct of the prosecutor, he found that nothing that had been done had, in fact, tainted the evidence given by the complainant. Although the complainant had been shown a photograph of the accused, he hadn’t changed his evidence as a result. The application was refused.
The Court provided a very useful discussion of the differences between preparation and coaching [beginning at 29]:
The difference between proofing and coaching
In R v Momodou  EWCA Crim 177;  2 All ER 571;  1 WLR 3442, Judge LJ, in delivering the judgment of the Court of Appeal of England and Wales, said:
There is a dramatic distinction between witness training or coaching, and witness familiarisation. Training or coaching for witnesses in criminal proceedings (whether for prosecution or defence) is not permitted. This is the logical consequence of the well-known principle that discussions between witnesses should not take place, and that the statements and proofs of one witness should not be disclosed to any other witness: see <R v Richardson  2 QB 484, R v Arif The Times, 22 June 1993, R v Skinner (1993) 99 Cr App R 212 and R v Shaw  EWCA Crim 3004. The witness should give his or her own evidence, so far as practicable uninfluenced by what anyone else has said, whether in formal discussions or informal conversations. The rule reduces, indeed hopefully avoids, any possibility that one witness may tailor his evidence in the light of what anyone else said, and equally, avoids any unfounded perception that he may have done so .
Whether preparation amounts to ‘coaching’ is inevitably a matter of degree, and is dependent on the facts: Re Equiticorp Finance Ltd; Ex parte Brock (No 2) (1992) 27 NSWLR 391, 395 (Young J). It is clear that the practice of witnesses reading their statements prepared contemporaneously with, or soon after, the incident in respect of which he or she is asked to testify prior to the hearing, or being taken through it by the person to whom it was made, is generally proper: <R v Richardson  2 QB 484,  2 All ER 773 (CA); R v Pachonick  2 NSWLR 86; Worley v Bentley  2 All ER 449; Mancorp Pty Ltd v Baulderstone Pty Ltd (1991) 57 SASR 87, 92 (Debelle J); see also Heydon J D, Cross on Evidence (8th Aust ed, 2010) . Moreover, it may be appropriate for solicitors or counsel for a party who is being called to give evidence to confer with the witness prior to giving evidence; in Re Equiticorp Finance Ltd; Ex parte Brock, Young J noted that:
It is clear that a witness might confer with his or her solicitor or counsel, or the solicitor or counsel for the party calling the witness, and that during such conference the solicitor or counsel concerned may give the witness advice. That advice may certainly include:
1) advice that the witness should refresh his or her memory from contemporaneous documents;
(2) directing the witness’ mind to the point about which questions may be asked;
(3) giving the witness a sketch of court procedure;
(4) directing the witness’ attention to points in his or her evidence which appear to be contradictory or fantastic;
(5) reminding the witness to bring to court all relevant documents;
(6) advising the witness as to the manner of answering questions (for example, ‘In cross-examination listen to the question, just answer the question asked with as concise an answer as possible’); and
(7) giving advice as to appropriate dress and grooming.
There may be other permitted areas (395).
Indeed, it has to be observed that in some situations, a brief discussion with a witness of his proposed evidence to clarify some point of ambiguity or uncertainty may be desirable in promoting the integrity and accuracy of the trial process: HKSAR v Tse Tat Fung  HKCA 156;  HKEC 815 .
Questioning of a witness moves beyond ‘proofing’ to impermissible ‘coaching’ when the witness’ true recollection of events is supplanted by another version suggested by the interviewer or other party, whether by repetitive reading of a statement to the point where their testimony is mere regurgitation or by otherwise influencing the witness: HKSAR v Tse Tat Fung; R v Momodou. A solicitor or counsel should not advise a witness as to how to answer a question: Re Equiticorp Finance Ltd; Ex parte Brock. By way of example, in Day v Perisher Blue Pty Ltd  NSWCA 110; (2005) 62 NSWLR 731 the defendant’s solicitors prepared an extensive document for the defendant outlining ‘possible areas of questioning, (to be passed on to the respective witnesses)’ and included suggestions as to appropriate responses which would be in line with the defendant’s case . This conduct, alongside the holding of a pre-trial conference by the practitioner in which multiple witnesses jointly discussed evidence to be given at trial, was held to seriously undermine the trial and ‘tainted’ the defendant’s case .
It is well established that the danger of suggestion is acute when the witness being interviewed is a child, and that for this reason it is particularly important that persons investigating sexual offences involving children avoid questions that are leading in substance: C v Minister of Community Welfare (1989) 52 SASR 304; Hardwick v The State of Western Australia  WASCA 164; (2011) 211 A Crim R 349 ; SJX v The State of Western Australia  WASCA 243.
The Court of Appeal was critical of the prosecutor (as the judge hearing the application for a permanent stay had been, too) for showing the complainant a photograph of the accused (in circumstances where the child had not seen it before, no formal process of identification had been undertaken, and the child’s description was at odds with the appearance of the accused). But as that had not changed the complainant’s evidence, the Court concluded that the appellant had not suffered any prejudice as a result. The appeal was dismissed.