It may be necessary for the prosecution to disclose to the defence information about prosecution witnesses concerning warnings that they have received from the police about their conduct, and about measures alternative to prosecution (eg diversion) that such witnesses have undergone: HM Advocate v Murtagh  UKPC 36 (3 August 2009), para 40(iv).
Such disclosure would be required if, as with any criminal convictions, that information would be material in the sense that it would either undermine the case for the prosecution or assist the case for the defence.
The decision on disclosure is, in current Scottish law, governed by the common law and is a matter for the prosecutor. Cases noted here and mentioned in Murtagh are Holland v HM Advocate (25.5.05), Sinclair v HM Advocate (24.5.07) and McDonald v HM Advocate (21.10.08).
The leading judgment in Murtagh was delivered by Lord Hope, and the only real point of some divergence was on whether it would be preferable for the prosecutor to disclose all the convictions of prosecution witnesses unless those convictions would be both embarrassing and immaterial (Lord Scott 43, Lord Brown 73).
While the common law does not require the prosecution to disclose information about the convictions of witnesses it knows the defence will or may call, Lord Rodger noted (70) that such disclosure would be consistent with equality of arms.
The accused's fair trial right is absolute and is not a matter for balancing against the privacy interests of a third party: Lord Scott (43; there was no disagreement on this). Criminal records held by the authorities can attract privacy interests, especially if they are old, so full disclosure is not an absolute right (Lord Hope at 18, 28). So, although the right to a fair trial is absolute, the right to disclosure is qualified (29).
Material convictions go to the witness's credibility or character (Lord Hope, 30) and a generous interpretation of what might be relevant should be taken, although a threshold applies (31). There are practical problems with the full disclosure approach favoured by Lord Scott and Lord Brown, such as the potential for harassment and other misuse of them by unrepresented defendants (33). There is no requirement of disclosure of the records of defence witnesses (39).
Lord Rodger emphasised the undesirability of redacting lists given to the defence, as that process can be time consuming (59) and can lead to disputes (69). Where disputes do arise, the judge should resolve them (69, and Lord Brown at 73), although Lord Hope saw no need for the disclosure decision to be transferred to some other party (15).
Disclosure of warnings and incidents of diversion from prosecution is not specified in recent legislation in New Zealand, the Criminal Disclosure Act 2008, although it would probably come within s 13(2)(a) which requires disclosure of "any relevant information", and the specified matters do not limit that expression.