Evidence of pre-trial correspondence can be adduced if it is relevant to a fact in issue, and not excluded by another rule of evidence. Commonly, pre-trial correspondence is not relevant to a fact in issue, because it consists of legal argument and rhetoric. In other words, the letter is the solicitor's inadmissible opinion. And when pre-trial correspondence does set out the facts, they are likely to be in the form of inadmissible hearsay.
Pre-trial correspondence is also likely to attract without prejudice privilege (if sent to the other side in an attempt to negotiate a settlement) or legal professional privilege (if private between a party and their lawyer). For all of these reasons, pre-trial correspondence is not usually considered by a judge or jury at trial.
However, in some circumstances pre-trial correspondence is admissible, typically as an admission, prior consistent statement or prior inconsistent statement. Depending on the facts which make the correspondence relevant and admissible, it may also be appropriate to cross-examine the client, a director or other agent of the client who instructed the solicitor, or the solicitor, about it.
In some cases, a client may be cross-examined about a prior statement of their solicitor on the basis that the solicitor would not have made the statement without the client's authority, and would have relied on the client's instructions. If the client changes their evidence, the prior inconsistent statement made on their behalf may damage their credibility.
If the client asserts legal professional privilege, or testifies that the solicitor acted without instructions, difficult questions arise. Some of these questions were explored by the High Court of Australia in Hofer v The Queen [2021] HCA 36.
In rare cases, a solicitor may be called to give evidence to resolve a dispute about whether a previous representation was actually made or authorised. This is, for example, the purpose of having a solicitor or other reputable professional witness a formal declaration. Cross-examination is typically only necessary to resolve an allegation of dishonesty or forgery.
The Court of Appeal of England and Wales dismissed an application for leave to cross-examine a solicitor, by applying the rules of evidence concerning prior consistent statements, in Hall v The Queen [2015] EWCA Crim 581.