The local Viking Challenge is in October each year http://www.vikingchallenge.org.uk/
UCI for all the gen in the world of top class cycling; road, mountain bike, bmx, cyclo cross http://www.uci.ch/templates/UCI/UCI8/layout.asp?MenuId=MTYzMDQ&LangId=1
The local moutain bike race series FNSS has ended. Check out http://fnssmtb.com/ for the results!
Or find an organised ride that suits you - http://www.bike-events.co.uk/