The Rule of Collateral Finality in Criminal Law

The rule of ‘collateral finality’ applies to the cross-examination of non-defendant witnesses in criminal proceedings. The rule is one of many important rules governing the procedure of criminal evidence in proceedings.

Under the collateral finality rule, the answers of a witness given under cross-examination on collateral issues are to be taken as final. If a witness’s answer is incorrect, the party cross-examining the witness cannot attempt to establish the contrary – they are not allowed to use any further evidence to rebut what the witness has said. This includes asking further questions, calling other witnesses to testify to the contrary, or providing documentary evidence.

That said, the judge or jury – as the ‘tribunal of fact’ – are under no obligation to accept the truth of the witness’s answer – and it could undergo further scrutiny further in the proceedings (if permitted in the particular circumstances).

What is the philosophy behind the rule?

If issues that are collateral to the main issues in the case are pursued without any restriction, the case could potentially go on endlessly. The rule restricts such questioning on collateral issues (subject to certain exceptions) to prevent the court’s time being wasted in establishing issues that are not material to the case. It encourages lawyers to focus on the essential issues of the proceedings by giving less weight to collateral (less important) matters.

In addition, the rule recognises it would be unfair to ambush a witness with questioning on issues that he had not anticipated.

What is a ‘collateral’ issue?

For the purposes of this rule, collateral issues are issues which are not directly relevant to the facts in issue of the case. Whether or nota matter is relevant to a fact in issue in the case depends on whether the information goes to the root of an issue in the proceedings.

Collateral issues could be both matters relating to the credibility of a witness, and establishing factual issues in relation to the witness. For example,if the issue in the case concerns the whereabouts of the witness in the evening in question, it would be immaterial to establish whether he took the bus or walked to work. Therefore, it would be viewed as a collateral issue and the restriction on further cross-examination would apply.

Whether the issue is collateral or not is a decision to be made by the judge. In the event of an appeal, the Court of Appeal will only interfere with the judge’s decision if it is wrong in principle, or was clearly wrong on the facts.

Are there any exceptions to the rule?

Yes, there are four categories of information/evidence which are exempt from the general rule of collateral finality:

  • Previous convictions
  • Establishing bias
  • Reputation for untruthfulness
  • Disability affecting reliability

If a witness is being cross-examined on a collateral issue that falls within any of these exceptions, the party seeking to establish the relevant facts is allowed, for instance, to produce any evidence available to contradict the answers of the witness giving live testimony.

Previous convictions

Under section 6 of the Criminal Procedure Act 1865 (applicable to both criminal and civil cases), where a witness answers questions put to him while giving evidence denies having a previous conviction or refuses to answer such a question, he can be cross-examined upon that conviction. In practice, a certificate from the convicting court is usually admissible to prove the previous conviction.

However, note that in relation to spent convictions, the prosecutors are not allowed to refer to them without the court’s permission.


Where a witness denies a suggestion of bias or partiality during cross-examination, evidence to contradict that statement may be called to show that he is prejudiced. In practice, in many cases it is material to establish motive to support or negate certain evidence.

Evidence of reputation to be untruthful

Evidence is admissible that a witness called by the opponent bears such a general reputation for untruthfulness that he is unworthy of belief.This exception is less popular in practice than the other ones,in particular since there are other provisions regulating the use of bad character of witnesses in the course of the proceedings.

Evidence of disability affecting reliability

Under this exception, medical evidence is admissible to show that a witness suffers from a physical or mental disability that affects the reliability of his evidence.The evidence is not restricted to a general opinion of the unreliability of the witness in the particular circumstances. It may extend further to include evidence of the foundations of the diagnosis and the extent to which the credibility of the witness could be affected.

Article written by...
Nicola Laver LLB
Nicola Laver LLB

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A non-practising solicitor, Nicola is also a fully qualified journalist. For the past 20 years, she has worked as a legal journalist, editor and author.