TSL Timing's diary is good for events they're doing the timing for. You can usually find the full line-up and a timetable close to the day. You could also try the organising clubs' own websites for further info.
http://www.tsl-timing.com/?loc=diary
Also a few more UK events listed at MST World...
http://www.mstworld.com/msportrounds...2010&series=UK
Calendar of the British Hill Climb Championship events here:
http://www.top12runoff.co.uk/