This one was at golding barn in West Sussex.....VERY hard chalk and clay soil in a natural bowl in the south downs. It was a yamaha off road experience day. I've also done similar at Wildtracks up near newmarket, with Geoff Mayes.
Of the two I'd recommend Geoff Mayes more at He's great!
The yamaha guys were ok, bit full of themselves and I found the fella who ran it (Barry something) a bit of a twat. Having said that you can ignore him and just enjoy yourself! They can be found at
As far as your road riding is concerned a bit of MX is definitely good for it, teaches you how to react when your bike gets out of shape and it's generally a fairly painless environment to crash in!