No problems at all returning the bras. Was the same lovely lady on the till as yesterday. Guess it depends on the staff in the shop...
Anyways, after giving myself a crash course on troubleshooting bra fitting last night, I ended up going down a band size and up two cup sizes - the 34B turned into a 32D....
That's just so much more comfortable.
Lesson learnt here is the following: just because you measure up as a particular size, don't assume that the bra of that size will fit / be comfortable. The pinching straps meant that the band was too big and the side spill was... well yeah...
We'll see how we get on with these. But as I said upthread, I'm going to keep looking regardless.