Rowan, send a copy of the death cert to the bank addressed to the Bereavement Dept. i would suggest
Dear Sirs
Re Dave Smith
Formerly of 10 Acacia Ave, Anytown
Date of death: 20 June 2018
Account No: 123456
I am administering the estate of my late husband who died on 20 June 2018. I enclose a certified copy of the death certificate for noting in your records and return, please. My husband died intestate and I am on the only beneficiary/my husband left a Will dated * which appoints me the sole executrix and beneficiary. I do not propose to obtain a Grant of letters of Administration in view of the size of his estate.
My husband held an account with you numbered 123456. Please would you arrange to close this account and forward the balance to me. Please also provide details of any income over the last year and whether any tax has been deducted.
Yours
rowanwitch
Now, they may just send you a cheque or they may ask you to fill in another form. I had mixed results when I was administering Mr BM's dad's estate. That letter worked with some (ie cheque just sent) but rather irritatingly not with one.