First of all, write to your contractor (politely!) advising of the defects, and asking him to contact you within five working days. Send trhe letter Recorded Delivery, and keep a copy. If that fails, send another advising proposed (and make sure you stress the 'proposed' bit) legal action if no attempt is made to rectify the unsatisfactory work. Again, keep a copy. If that produces no action you have two choices - visit your Citizens' Advice Bureau for advice on suing the contractor through the Small Claims Court, or, less hassle, but potentially more expensive, get a good solicitor. Hopefully, the second course of action won't be necessary, but in all dealings, remain calm and polite, remember, he's got your money, and you are either going to have to be nice, or be legal, to get it back. Good luck.