I had to do exactly this, and I had to get powers of Deputy in the Court of protection.
I warn you - you have to do this, and it may take up to 2 years. If you don't do it, the Court of Protection may step in and appoint a solicitor, who will have to pay himself/herself out of your father's funds. Search "Court of Protection" on the Internet and follow all instructions, print off all forms, send them off and wait. There will have to be forms from doctors, consultants, psycho-geriatricians, and Uncle-Tom-Cobbley-and-all. maybe also Social workers, nurses, Home manager . If all else fails, go to the Citizens Advice.