[Sundae]

I know nothing about this situation, but I do feel your pain.

No UK supermarket/ High Street Store will accept a cheque as a valid form of payment.
They may still do so online or for some bills. But I don't have a cheque book, so I'm hazy on details (not issued on my account any more).

I pay a debt every month over the counter at the Post Office IN CASH and a 50p charge is added. AND it takes 3 days to clear. Wait, what?
50p is not much, but it's a bloody cheek given the clearance time.
It would be higher if I paid using my debit card.

Oh and I can't get money over the counter from my own bank.
Well - I can. But it has to be over £100 (which I never have to spare). And over a certain amount (which I have not memorisied as it is so unlikely) I have to contact them in advance anyway.

So if I have £9.99 balance I have to go to the Post Office to withdraw it because the minimum amount from an ATM is £10.
Why is going to the Post Office worse than going to the bank?
If you have to ask, you've obviously never queued in an English Post Office. My experience? Minimum 20 minute wait.