I've not read the whole thread, but have been dipping in and out (seems appropriate )
Meant to say this earlier but didn't have time to post.
What I've seen suggested previously, using POA, is leave him with access to his current account, with a small amount of money in which you top up (weekly monthly etc) but transfer all of his savings to another account which he can't access.
Certainly when I registered mum's POA, every bank asked if she still had capacity, at the time, she did and I said yes to the one's she used the cheque book on (no longer capable of operating a bank card at the time). Others I said no, as I thought this provided better security for mum. (she had limited capacity - enough to deal with a cheque book but not enough to understand a bank statement to be honest). I did what worked for mum at the time, but this might give you some thoughts as to how to deal with it.
So what I am suggesting is you can tell the bank with current account he has capacity, and the open a seperate account at another bank (using POA) and say he doesn't have capacity. If you think you can get away with this.
Banks legally have to freeze a PWD's access to their own accounts it they believe the PWD doesn't have capacity so needs to be done carefully.