From the information my son has managed to get from his father it seems he (his father, no other beneficiaries) want to use the wishes set out in the unsigned will, as that was the most recent,

He might want that, but if the “latest will” was unsigned, it isn’t a valid will, just a piece of paper.

Thank you honeybee, I was under the impression probate is basically an application to authenticate the will and for permission to gather together everything the estate has. Until probate has been granted to the executors you have no right to do anything, certainly not take money from the deceased bank account.

Not quite. You are correct that Probate is the state authenticating the Will and formally confirming who is authorised to administer the Estate, that the Will is correctly drawn up in the form required by law etc. However it isn't the case that Executors have no power to act until Probate is granted - for very small Estates there may be no need to apply for Probate at all. The Exceutor has the legal power to act from date of death. However third parties (banks etc) are not required to accept the Executors instructions until Probate is granted. In practice for an Estate of any size an Executor cannot do anything much without Probate simply because banks and other institutions will refuse to deal with him until he has the deed of probate.

Banks will allow money to be withdrawn from the Estate for limited purposes before Probate is granted - normally only to pay funeral expenses and to pay IHT.

But I know of case in my family where deceased's brother had obtained the deceased's debit card and PIN number and withdrew money before bank knew that deceased was deceased.

The estate is probably in the region of about 2 million, 1 transaction 2 days after FIL's passing was for £30,000, funny how he acquired camper van not long after.

I'm pretty sure there's some dodgy stuff going on and I'm sure he'll get caught out eventually.