ppeat I suspect she won't be accessing that account for long ... He could get the statements (and who still gets paper ones anyway?) delivered to the shop or another address, or intercept them, and her bank card could go the same way as the cheque book, perhaps?
Interesting thought about him having an affair. I wonder who with? There's not really anyone else middle class available of the right sort of age, is there? Alice is the only candidate I can think of.