Isn't there a Debenhams in Oxford? They do the not-actual-measuring thing, where you try a bra on & they look & say why it doesn't fit & suggest a better size (repeat until fits). Major advantage: no one waving a tape measure around your norks, although you do still have to stand around in your bra in front of them, albeit briefly. This is also apparently more accurate than the measuring tape calculations.

(I do it myself now: band should be level all the way round & pretty tight; underwire if existent flat against ribcage all the way round each boob; nothing sticking out. The hit rate is still about 3 or 4 that I get on with out of 10 or 12 tried on, but at least the ones I get on with do *actually fit* which is a novelty.)