Well specificly for your usergroup you will need to first click on the following link
Click the JOIN button. The group moderator Grant R will then get a notice that you want to join his group. Once your approved you will should get an e-mail notifying you that your request had been approved.
THen you can start posting over there.
BTW if you see other UK members and I know we have them here make sure they know about the UK forums so you all can chat about UK stuff.