"34. Effect of accused's failure to mention facts when questioned or charged (1) Where, in any proceedings against a person for an offence, evidence is given that the accused — (a) at any time before he was charged with the offence, on being questioned under caution by a constable trying to discover whether or by whom the offence had been committed, failed to mention any fact relied on in his defence in those proceedings; … being a fact which in the circumstances existing at the time the accused could reasonably have been expected to mention when so questioned, … subsection (2) below applies. (2) Where this subsection applies — ... (d) the court or jury, in determining whether the accused is guilty of the offence charged, may draw such inferences from the failure as appear proper."
"The time referred to is the time of questioning, and account must be taken of all the relevant circumstances existing at that time. The courts should not construe the expression 'in the circumstances' restrictively: matters such as time of day, the defendant’s age, experience, mental capacity, state of health, sobriety, tiredness, knowledge, personality and legal advice are all part of the relevant circumstances; and those are only examples of things which may be relevant. When reference is made to 'the accused' attention is directed not to some hypothetical, reasonable accused of ordinary phlegm and fortitude but to the actual accused with such qualities, apprehensions, knowledge and advice as he is shown to have had at the time. It is for the jury to decide whether the fact (or facts) which the defendant has relied on in his defence in the criminal trial, but which he had not mentioned when questioned under caution before charge by the constable investigating the alleged offence for which the defendant is being tried, is (or are) a fact (or facts) which in the circumstances as they actually existed the actual defendant could reasonably have been expected to mention. Like so many other questions in criminal trials this is a question to be resolved by the jury in the exercise of their collective commonsense, experience and understanding of human nature."