In reply to Rob Exile Ward:
Depends what you're doing. There's nowhere in any law that says things have to be PAT tested. There are laws saying that things should be safe (different ones apply depending on what you're doing) and PAT testing is widely seen to be a way of complying with this (and if something explodes after being PAT tested, the fact that you PAT tested it is one way of claiming it was being properly maintained).