We've set up a mountain bike club in Swindon. We also have our own single track trail that we're working on.
See http://www.mbswindon.co.uk for more info.
March news update: http://www.mbswindon.co.uk/185/
We have a ride and build event for March 13th organised in conjunction with settingascene.com:
See their website at http://settingascene.com/viewtopic.php?f=51&t=448#p2575 for more info.