In reply to UKC Gear:
"For me these are a bit of a conundrum when it comes to fit. I'm usually a size 5 ½ but I had to go for a size 6 – which proved to be vice-like rather than glove-like. I can't need a whole size larger can I?"
Well, probably, yes.
I think anyone new to climbing should just ignore the label size. I climb in size 39s and in 42s from different brands, and both are good fits. It doesn't really matter what you "normally wear" because rock shoes from various brands aren't normal.
The more shoes I have owned over the years, the more I'm convinced that unless you are just buying like for like, you need to go to shop and try shoes on until you find the ones that fit. Ignore the size label besides as a starting point.