It's returning GBP perfectly for me at the moment, so maybe it was a temporary glitch?

If this part of the tool is just calling the Travelocity fare listings, which I suspect it is, whether you get USD or GBP can be a bit hit-and-miss. It seems to depend on when you last logged in to Travelocity and to what level. Sometimes it resets from USD to GBP only after making a dummy booking and cancelling at a very late stage, closing the browser window and then restarting. I've got quite used to having a currency converter window open at the same time when it's misbehaving for me.