"...Where a witness whom the prosecution call or tender gives evidence in the box on a material issue, and the prosecution have in their possession an earlier statement from that witness substantially conflicting with such evidence, the prosecution should, at any rate, inform the defence of that fact: Rex v Howes (unreported),27 March 1950 , C.C.A...In certain cases, particularly where the discrepancy involves detail, as in identification by description, it may be difficult effectively to give such information to the defence without handing to them a copy of the earlier statement: Rex v Clarke(1930) 22 Cr. App. R. 58 ; see also Baksh v The Queen[1958] AC 167 ."