Hey matey. my brother has been doing kithcen and bathroom fitting for 20 years now without qualification. He doesn't touch gas obviously.
Think this link will give you a good idea of where to head personal development and qualifications wise.
Kitchen and Bathroom Fitter - learndirect*Careers Advice
Think the government are making some changes in the law to prevent "cowboy" tradesmen which should see a lot of changes by 2010. Perhaps someone else here who is more in the know can elaborate!
Nick