I am so sorry to hear about your Dad
I am assuming your Dad died as a result of the fire, do you have a Family Liason officer number to ring either at the police or fire brigade, if so try them.
Are you able to register your Dads death at the registary office, if so there is a helpful booklet available, ask if it isn't offered to you.
If your Dad was in receipt of a pension or other benefit ring the benefit office and ask to speak to someone regarding you Dads claim. All benefits are paid into a bank account the benefit office will tell you which bank it was paid to, may only be the post office bank but it is a start.
You say it was a council house again ask to see someone to see how the rent was paid and council tax, there maybe a direct debit..
Did your Dad have a pension or any payment from somewhere he had worked, again find out how it was paid.
If you cannot yet obtain a death certificate ask hospital, coroner, police etc for a letter to confirm your Dads' death to show benefit, council offices banks etc.
When you track down a bank account you may find a direct debit for an insurance company, if not do the council know [unlikely]. If not try ringing a Well known Insurance company, you may need to speak to a supervisor or underwriter, ask them if they know any way of tracking down an insurance, I have a feeling a lot share a data base to stop fraud likewise they could use this to help you.
Try to take someone with you, under the circumstances you are unlikely to remember everything you are told, ask for details to be wrote down for you, and take a list of the quwstions you want answering.
Do re=post or come back, if you are still unable to track anything down.