Darling BBB - you can earn miles but if you do it through the Travelex link on ba.com or at the airport you'll get an absolutely awful rate.

If you go to Travelex.com and do through there, without trying to claim miles, the rate is much, much better.

But there are other places in London where you can get really good rates. I know Victoria Street and Soho have a few places. I will try and find out from a few people on Monday night (you know where ) and let you know.