In 1893, the Judicial Council of the British House of Lords established a rule of evidentiary fairness; that:
"... it seems to me to be absolutely essential to the proper conduct of a cause, where it is intended to suggest that a witness is not speaking the truth on a particular point, to direct his attention to the fact by some questions put in cross-examination showing that the imputation is intended to be made, and not to take his evidence and pass it by as a matter altogether unchallenged, and then, when it is impossible for him to explain, but perhaps he might have been able to do it such questions have been put to him, and circumstances which it is suggested indicate that the story he tells ought not to be believed, to argue that he is a witness unworthy of credit.
"... if you intend to impeach a witness you are bound, whilst he is still in the box, to give him an opportunity of making any explanation which is open to him."
Simply put, when you have a witness on the stand during a trial and it is your intention to later in the trial, raise evidence that would contradict the witness, is only fair to the witness that you give him/her notice of contrary evidence so that he/she might then have an opportunity of addressing it.
In R v Werkman, Justice Côté of the Alberta Court of Appeal wrote:
"The rule in Browne v. Dunn requires that counsel put a matter to a witness involving the witness personally if counsel is later going to present contradictory evidence, or is going to impeach the witness’ credibility. Though it is not necessary to cross-examine upon minor details in the evidence, a witness should be provided with an opportunity to give evidence on “matters of substance” that will be contradicted. The purpose of the rule is to ensure that parties and witnesses are treated fairly; it is not a general or absolute rule. The rule also has exceptions."
This is not only fair to the witness but also more importantly, to justice as to omit to put contrary evidence to witness puts the presiding officer of the court in an undesirable position of recreating the truth without all the possible explanations otherwise available.
Like many rules of evidence, the rule is subject to a number of exceptions but it is otherwise held to apply in both civil or criminal cases.
REFERENCES:
Browne v Dunn 6 R. 67 (1893, House of Lords)
Peters v Perras 42 Supreme Couirt Reports 244 (Canada, 1909)
R v Werkman 2007 ABCA 130, published at canlii.org/en/ab/abca/doc/2007/2007abca130/2007abca130.html