Originally Posted by theworld
If you can't find the Bilbao try Thoms Global Exchange on Victoria St:
http://www.thomasexchangeglobal.co.uk/
Their rates are very good.
Re ATMs it really depends on which debit card you have (DON'T use a credit card in ATMs).
I've also got a Nationwide debit card and have used it many times in the states. I have only been charged once by a US bank. Many US banks like Wells Fargo, Bank of America and others don't charge a fee.
I was going to suggest them too. If you can't have a Nationwide Debit Card (and if you live outside the UK you can't), their commission-free rates (for
buying foreign currency at least) are about the best in London.