Had no idea of the best place to change our excess $US back to £GB, but a quick google (or should I say duckduck now?) offered NM Money as an interesting choice with a generous exchange rate. Simply set up the request online and pick up from Eurochange at Meadowhall the next morning. And they offered a significantly better rate than Eurochange themselves! How does that work?! Anyway, it does, and it did. Seemed too good to be true, but it was just brilliant.