Welcome to the forum, depending on how far you wish to travel for a race meeting you could try Norfolk Buggy Club, we based a little north of Norwich.
For more information and race dates check out our website
www.norfolkbuggyclub.moonfruit.com
You May also want to check out the regional website, a link is available from the NBC site, which I believe lists most of the off road clubs in the East of England Region.