snowfrog - please don't assume - he is providing a service - he is happily taking your money for that service.
If you dont know his name ask it, ask for a business card, take his van registration number, and take lots of pictures of his work. Get his details from your electrician friend, maybe he can help you? Have you given him an opportunity to refund you for the tiling work only? (if his plastering etc is good). You really need to take professional advice (which is free from OFT or your local CAB). don't procrastinate.