Sorry bit late with this Nick, but the start of the G10/42 is at the end of Spook Hill. A25 towards Dorking, left at the Deepdene RAB (the one with the giant cock in the middle), then left (1st exit) at the next RAB is Spook Hill. For evening 10s most park at the top of Inholms Lane (left by the church on Spook Hill) in the National Trust car park at the top of the hill on your right - the results are given out here at the end of the evening too.
The next one on the GS/355 is in Bletchingley and a Sporting course (read hilly - drag at start, nice long double downhill, then tough return section to the finish which has 2 hills and a noticable lump in between them, you finish at the top of the second hill.) as a warm up and course familiariser for the inter-club 10 againg Norwood Paragon. It's a bit longer than a 10 at just under 11 miles. That starts in Waterhouse Lane where you can also park or you can park in Bletchingley and roll down to the start.
The course is [url=http://bikeroutetoaster.com/Course.aspx?course=50914]here[/url] although for some reason it didn't want to show the elevation when I did it. It's easy to follow, straight up the main road to the pub after the motorway bridge, left there, then stay on the road to the end and left at the T junction. Then just keep going 'til you see people, at the top of the hills, through the spots in front of your eyes. Should be marshals at the turn points though.