Sure man anything for a british fellow
If you don't mind buying second hand a great guy on the forums is selling a GTX465 which has been unlocked to a 470 for Â£130.
Also a little over budget but here is a 5850 for Â£166.
I'd say it's really your choice between the GTX 460 and the 6850 if you're buying used. They both have similar performance and both have their advantages and disadvantages. It all comes down to personal preference really. Also, you can just about get a 5850 for Â£150, which performs better than both the GTX 460 and the 6850.
Edited by Ellis - 12/28/10 at 5:16pm