I was not asked to provide evidence that my wife had lost capacity when I registered LPA with her bank (the one with the dark equine). I did take a file full of paperwork but other than taking a photocopy of the LPA document it wasn't looked at. I had been managing my wife's finances for some time as she was no longer capable.
Hence it did not matter that her bank card and cheque book were stopped and a new card issued in my name. Telephone and internet banking was also changed to be accessible by me as Attorney, not my wife. She did not notice.
When it gets to that point
@vaana it will be much easier for you to keep on top of your father's financial affairs. At the moment I am guessing that any suggestion that he shouldn't manage his own affairs would not be welcomed and could be a source of stress and frustration. A situation where he was denied access to his own money when visiting his usual bank could be very distressing and disruptive.
But I think that you do need to try to get him to agree to you helping out with his finances. You might then be able to ensure that his available balance is kept low enough to prevent him just giving cash away.