Rickp, a few years ago, the proprietor of a BandB in Edinburgh accepted a personal check drawn in U.S. funds from our bank here in the States. It was held as deposit for our reservation, then returned to us upon our arrival.

You might ask your BandB if they would accept that arrangement.

Luv2Travel, when you are in London, use your bank ATM card. Do NOT use your credit card for cash advances; interest charges will begin the moment you withdraw the cash.

As Beany explained, the machine will process your transaction in GBP. As you input your info, you will be prompted for the number of GBP you are withdrawing. You should be aware of the approximate rate of exchange (and how much money you want to have on/in hand) before you begin the transaction.