Attorneys are in a position of trust and should always keep detailed records and accounts of their financial dealings for the donor. These can be asked for. Ultimately, a Civil Court action could be taken for damages.
If it was an enduring power of attorney it should have been registered at the Court of Protection when your father became mentally incapable. In that case, the Court can ask for the accounts to be produced. Go here:
http://www.guardianship.gov.uk/
to get some info. & then contact them.
If it was not an enduring power then it became invalid when your father became mentally incompetent and should not have been used.