Blinkz,
I would simply get stuck in at your local gliding club, a tuggie post will come your way if your keen enough. You already have some gliding experience which will stand you in good stead. We have a handful of tuggies that all turned up "on spec" and all were taken on. If you dont ask you dont get! As for A/C, not all clubs use pawnee's, many use Robin's, Rallye's or even Chippies and Cubs. Most of the pawnee clubs I know also have a spare 2/4 seater for tuggie training and annual checks etc. Most clubs are all on the internet with their own web pages. Try the British Gliding Assosciation website and you'll find a list of all the UK clubs and any that are near you. The club web pages usually have a list of their A/C fleet too.
Mike