For someone starting out I would say electric is much easier and therefore as Chris has said TORCH is your nearest plus as dudders mentioned you've got Surrey and Hants too.
Also down at Three Legged Cross is another off road electric track, it's more bashing than racing with Electric Truggies ( a cross between a truck and a buggy ),
LINK, that's just down the road from me but I'd rather go to Clanfield to race as it's better, you could pop down there this Sunday as it's being reopened but work is still being done on it so I don't know when it will be fully open again. It will give you an idea of what's going on and you can talk to people about the cars they're driving.
All that said I think apart from the locations suggested you should sell the bike and get a basic buggy to get you going with the electrics. TORCH is also running that day so maybe you could get to there and Clanfield in one day... give yourself a real idea of what it's like.