Last time I went here for the day it cost £15 to ride my bike around their enduro course for the day. Peter Knight who runs it is a good bloke who I am sure would entertain a large group of us, probably sort stuff like BBQs and first aid for us !!
I have also been on one of their experience day ...

How about one of the tracks that ESSEX off road operate, the one near Epping forest, 5 minutes off the M11 is not bad.

http://www.essexoffroadexperience

Tell us where tell us when.....I will be there