I bought GF a caterham slalom day for his 30th, directly through Caterham. There was a choice of venues, we went to Silverstone. Would thoroughly recommend it, it was a great day, he really enjoyed it.
there were no where near as many people on his day as lord s mentions above, maybe 10? It seemed much better vfm than most other car days I looked at. I booked it after recommendataions from a few people on here.