frontline has a monthly walk on first sunday of month.
at leisure lakes near southport.
3000, 4500 air and co2.
see http://www.frontlinepaintball.co.uk/
and checkout the forum.
I went to Bawtry for the Easter Egg Hunt walkon- a great day, lots of games on some very impressive fields. The towers field is like nothing I've ever seen, and a very friendly bunch with useful bits for sale from Big Dicks as well.