With Buckmore the organiser needs to pay in full up front. I've tried to organise events there but I'm not putting a load of my own dough down in case people can't turn up, cancel etc.
I much prefer the atmosphere and staff at
http://www.bayfordkarting.co.uk in Sittingbourne. Really relaxed, decent karts and a fun, fast circuit plus everyone pays on the night. A fair amount cheaper than Buckmore too. I've organised I think 3-4 events there in the last 2 years and they've always been great fun.