in M&S and lasenza, they measured me under the bust, which was 27″, then they tried bras on, they both started with a 32DD and worked up to an F in M&S and an FF in lasenza.
im a 32f in all shops, and also primarni have started to do some of their animal print range in a 32F which are so comfy and a cheap alternative to constantly buying la senza and M&S xxxx