If he doesn't want to talk, that's within his rights
This is true in the US. It's not quite true here in Australia - a refusal to talk to police can be used against you in a court of law. It's not going to make or break a case, but you can't just 'plead the 5th' here and have no consequences. I imagine it's similar in the UK as our law is quite similar to theirs.
"You do not have to say anything, but it may harm your defence if you do not mention, when questioned, something which you later rely on in court. Anything you do say may be given in evidence."
This is true in the US. It's not quite true here in Australia - a refusal to talk to police can be used against you in a court of law. It's not going to make or break a case, but you can't just 'plead the 5th' here and have no consequences. I imagine it's similar in the UK as our law is quite similar to theirs.