Although for an out-of-court admission to be conclusive of guilt it must be in writing, a properly obtained oral admission - that is, 'any statement wholly or partly adverse to the defendant' - is indeed admissible in court, as an exception to the rule excluding hearsay in evidence. In general terms, a confession only becomes clearly inadmissible if the prosecution fails to establish that it was properly obtained. And, as for corroboration, an admission by a defendant may itself be used as corroborative evidence to support other more circumstantial evidence.
Mr Powell goes on to claim that if a suspect is innocent 'the chances are he has nothing useful to contribute', suggesting that this is another reason to keep silent. As someone who once advised suspects at police stations, I find such an attitude dangerous. Although things are rarely so clear-cut, if, after speaking with a legal adviser, an innocent suspect is confident that he can clear up the situation by speaking, it is surely in both his and the police's interests that he does so. He thereby ensures that neither his nor the police's time is further wasted.
PIPPA R. HOLMES