when you declare bankruptcy virtually all banks will automatically freeze the account. When the Official Receiver advises the bank that they have no interest in the funds which were in the account at the time then the account is unfrozen, you withdraw the funds and the bank will close the account permanently. If there were no funds in the first place the bank could go straight for closure.
If the frozen funds are not proven by you, whilst in a frozen state, to be for essential living expenses the OR will claim the funds as part of your estate.