I would send a copy of the will, a copy of the document from the solicitor and a letter from you as executor. That should be enough. I wouldn't pay for certified copies at this time.

I know, I stated that in my earlier post. The biggest concern is funding terrorism

I would even recommend against that - customers asking "awkward questions" under this sort of circumstance are likely to be referred internally for review and investigation (by the bank/loan company's Compliance department) for possible, and I would suggest likely, referral via a Suspicious Activity Report, as I described above. The reason being, that it looks like they have something to hide.

And I believe that you are incorrect because if the loan has already been disbursed it is too late to counter with another loan offer.
Not really, though you might think so if you relied on the mainstream media. Money laundering is a much wider issue than that, and it catches out a LOT of innocent individuals in collateral damage. Many of those are people who try to be smart-är§es, färt around with their transactions, or asking questions about the reason for information being requested.

I like living on the edge lol.

As executor, didn't you have to file a UK Revenue form R185 (statement of income from estates)? That has the distribution of the estate as an attachment and would provide the information you need.