The Solicitors' Practice Rules impose a variety of duties on solicitors. In this case - where your client has specifically told you he committed the crime (NOT where you merely suspect that he did*) the rules put you in a difficult position. Your overriding duty is to act in the best interests of your client. However, you also have a duty to not mislead the court. So, in these circumstances there are limits on what you can say on your client's behalf in court. You *can* 'put the prosecution to proof' - cross examining its witnesses and seeing how well its case holds up; if the prosecution can't prove its case beyond reasonable doubt then your client will be found not guilty. What you can't do is say anything to the court to mislead it eg. you can't assert your client's innocence while cross examining prosecution/other defendants' witnesses, nor can you present any form of defence to the court.

If after admitting his guilt to you your client insists that he wants to plead not guilty and enter a substantive defence you *must* decline to act. You can't tell the court why you have withdrawn - you resort a catch-all phrase like 'for professional reasons' (there are other rules of conduct that can force you to withdraw from a case), because you still have to act in the best interests of your client.

If you merely suspect that your client is guilty (but don't *know* this to be the case) then you are free to say whatever you like in his defence ie. you can assert his innocence/put forward a defence.

I don't know the details of the rules that bind barristers but I believe they mirror these provisions.

Prod me with a cluestick if this doesn't make sense. We were looking at this on Monday and it's fairly fresh in my mind, but I'm not sure how lay reader friendly I've managed to make it.