I have used the trousers in warm caves in Mexico and they were very good, drying out quickly and keeping me cool. I wore a thermal top and leggings underneath and the only problem was that the top would get caught on cave walls and such like but I suppose you just have to accept that! I'd imagine that the top would be useful if you started to get cold but I think that with all the wriggling around in British caves, that a one piece suit would be better and less likely to get damaged.
Lots of American cavers use these trousers quite a lot too so they must be okay