I'm not entirely sure that's the case. The guy is the CEO.
So let's say he can't access it from the UK. The UK guys tell him "give us the documents or you go to jail". Well then he could ask an employee who is currently in the US to unlock them for him, maybe even give them his password. Basically, there is usually a way to get things done if there is a threat of jail pending.
The greater issue is how the UK was allowed to even do something like this to a person who hadn't done anything illegal.