Bank

[Workingman]

Still sounds dodgy. I cannot find any level of such payments for things like pension credits, HMRC, Universal credit, etc.
Government version:

Transactions
If you have an enquiry about a transaction you have received, you will need to go back to your bank and request that they provide you with the full name of the payee.

Personally I would want to know from whom (which department) and why a mysterious £425 suddenly appeared in my account just in case they "suddenly" wanted it back, but it's up to you, Vic.

[cruiser2]

I will be checking my bank statement later.

I just get the State ension paid in every four weeks. There is also the £100 payment usually in early December.

[victor]

Mystery solved,it is winning Premium Bonds,which we did not consider as we did not receive the usual email notification of being winners

[TheOstrich]

Blimey, Vic, you've won more in a month than I've won in a lifetime!!