On old case on the difficulty of telling whether a witness is lying or telling the truth. Lord Greene M.R. said,

‘Puisne judges would be the last persons to lay claim to infallibility, even in assessing the demeanour of a witness. The most experienced judge may, albeit rarely, be deceived by a clever liar, or led to form an unfavourable opinion of an honest witness, and may express his view that his demeanour was excellent or bad as the case may be. Most experienced counsel can, I have no doubt, recall at least one case where this has happened to their knowledge. I may further point out that an impression as to the demeanour of a witness ought not to be adopted by a trial judge without testing it against the whole of the evidence of the witness in question. If it can be demonstrated to conviction that a witness whose demeanour has been praised by the trial judge has on some collateral matter deliberately given an untrue answer, the favourable view formed by the judge as to his demeanour must necessarily lose its value.

There is one further consideration which is particularly relevant to the present case. A judge who observes the demeanour of the witnesses while they are being examined by counsel has from his detached position a much more favourable opportunity of forming a just appreciation than a judge who himself conducts the examination.’

From [pp. 19-20]