In reply to WeeTJ: It's a tricky one.
In an ideal world a lot of UK climbers would ideally have three (or more) different ropes:
A short 30-40m cragging/indoor rope.
50-60m, double ropes for multi-pitch (probably dry treated, possibly shared one each with a partner)).
A good quality, thin, 60m (or even 70m) sport climbing rope.
What this means is that is you are going to be stuck with one rope for the foreseeable future then a 10mm x 50m single is going to be the best compromise. Unfortunately, as a compromise it will almost never be ideal. The bulk of the time it will be too long, but conversely it will probably be too short and a bit thick to double up and for some sport climbing destinations. You will also invariably want double ropes at some point for more adventurous multi-pitch.
My default rope is my short single. It is far cheaper (and lighter) than my other ropes so if possible I will always use it where I can. I find I can use it for a surprising amount of my climbing - indoors, most gritstone and single pitch cragging, over half of my UK sport climbs, scrambling and easier multi-pitch, winter ridges and even dry-tooling.
Therefore, if your local venues tend towards shorter pitches it is certainly not unreasonable to think about buying a cheaper, shorter single initially but with a view to then purchasing a half rope(s) or a much thinner 60m single sooner than you might otherwise.
Anyway, good luck and climb safe.