In reply to 3leggeddog:
We are off to Gorge Du Tarn in August which has been recommended by several friends as a good summer venue, we got flights from a local airport (Southampton) and then a 2-3 hour drive the other side so well within your 10 hour travel window, or you can Ferry and drive but that will weigh in at considerably longer, especially if you are in the North of England.
I don't know what grade you climb but it's a little thin on the ground in the lower grades, with much more interest in the 7's and above, so that might be a deal breaker.