I agree with Lissa, I did the below in a week (starting in Belgium mind) and averaged some big miles (over 2000 in 6 days), a lot on twisties:
http://forums.sv650.org/showthread.php?t=82336
However the UK can be quite built up in places and it is this and getting lost that can slow you down.
Hope you have a great time and see parts of the UK that you'd never imagined existed.