U. S. banks by law are not permitted to deal in foreign currencies unless they are a federal reserve bank. Only a few of those.
It is a nuisance, but unavoidable.
The bank can bag your furrin money and send it, at considerable expense and with forms explaining the source, to a federal reserve, so only larger amounts, and no coin please, are pay the costs.


Mastercard, Visa, etc. have made it easy if the UK or U. S. business accepts them. There are outfits like Paypal and Moneybookers, but I have never dealt with them.

Canada is easier, UK sterling or American dollars. I buy UK sterling money orders at my bank for purchases from UK in those cases where the seller does not take plastic.
I received a refund in Euro currency from a fellow in Germany, and the bank would not accept it, so I had to send it back.
Canadian banks are not prohibited from dealing in foreign currencies, but there are restrictions that make some payments costly.