Have a look at Condor Cycles website - they make a fast tourer/randonee bike that sells very well. The other option is SJS cycles which seems to have a very good reputation.
Also, have a chat with the people in the touring forum here.
http://www.condorcycles.com/ - quite possibly the best bike shop in London
http://www.sjscycles.co.uk/
http://www.bikeforums.net/forumdisplay.php?f=47