Thank you for all your replies. The tiler who laid these tiles was an expert tiler(unfortunately now decesed) and I would have paid for anything that he suggested so I would be surprised if the membrane wasn't applied. The suppliers(supposedly reputable) stated that the tiles were suitable for indoor and outdoor and under floor heating. Is there any official body I can get to give a view on the whether these tiles are sub-standard as I now have a large area of cracked tiles with more cracks appearing by the day