A cautionary note from the Privy Council on the timing of a challenge to the defendant's fitness to stand trial: Taitt v The State (Trinidad and Tobago) [2012] UKPC 38, at [18]:
"In Nigel Brown v The State
[2012] UKPC 2, para 68 the Board expressed its concern at the fact that reports as to the appellant's ability to instruct counsel were produced ex post facto and without any explanation as to why medical evidence on the issue of fitness had not been produced in the courts below. It wished to make clear that it should not be assumed that even highly persuasive evidence produced for the first time at the final appeal stage would be admitted: para 70. The fresh evidence has been admitted in this case so that it may be scrutinised. But the Board is just as anxious to make it clear that it will only be in an exceptional case that it will entertain the argument that the appellant was not fit to stand trial because he is of low intelligence due to a learning disability when the point was not taken on his behalf by counsel at his trial. It is the responsibility of counsel to assess whether his client is fit to stand trial. He is in the best position to judge at first hand whether his client is able to understand the charge that has been brought against him and to give instructions for his defence. His conclusion that his client is fit to plead will normally be given great weight. The Board will not permit the introduction of the issue for the first time at the final stage unless the evidence points very clearly to the fact that there has been a miscarriage of justice."
A finding prior to or during a trial that a defendant is unfit to stand trial is usually, perhaps always, made on the balance of probabilities: see for example s 14(3) Criminal Procedure (Mentally Impaired Persons) Act 2003 [NZ]. Counsel may therefore be in the position of having to act for a client who only by a narrow margin fails to establish unfitness to plead. There will in such cases be a strong temptation, in the event of a conviction, to look for more persuasive evidence than was offered earlier to establish unfitness. The Privy Council recognises that where the issue was raised at first instance the position on appeal is quite different to that where the issue was not raised. A decision by experienced counsel not to raise at first instance the issue of fitness to plead will be given great weight. Raising the issue at first instance may require counsel to go against the client's wishes and to insist on expert assessment. Mentally impaired clients may be insulted by any suggestion of disability (recognised at [14] of Taitt). Here the obligation to follow instructions may be overtaken by the obligation to act in the client's best interests from the perspective of avoiding a conviction.[2012] UKPC 2, para 68 the Board expressed its concern at the fact that reports as to the appellant's ability to instruct counsel were produced ex post facto and without any explanation as to why medical evidence on the issue of fitness had not been produced in the courts below. It wished to make clear that it should not be assumed that even highly persuasive evidence produced for the first time at the final appeal stage would be admitted: para 70. The fresh evidence has been admitted in this case so that it may be scrutinised. But the Board is just as anxious to make it clear that it will only be in an exceptional case that it will entertain the argument that the appellant was not fit to stand trial because he is of low intelligence due to a learning disability when the point was not taken on his behalf by counsel at his trial. It is the responsibility of counsel to assess whether his client is fit to stand trial. He is in the best position to judge at first hand whether his client is able to understand the charge that has been brought against him and to give instructions for his defence. His conclusion that his client is fit to plead will normally be given great weight. The Board will not permit the introduction of the issue for the first time at the final stage unless the evidence points very clearly to the fact that there has been a miscarriage of justice."
