Have just been to a bra shop in Coventry called Butterfly Bras, on Spon Street. The lady measured me accurately (31.5") and said I should try 32E or 34D depending on how tightly the fit on each bra was. She showed me how to put my bra on and told me to make sure the whole of my breast was in the cup.
I ended up with 32E bras and she was lovely. Older lady too so didn't feel embarrassed.
Brilliant service!!