So sorry for what you’ve gone through, it’s wrong in a big way.Thank you so much for all the helpful advice. We've sent the tiler a letter detailing all the issues and so far had no response. Given the advice that he will be unable to resolve this, it does look like the most likely scenario is we need to find someone new to do the job properly. Does anyone have any experience / know any case studies of obtaining compensation / winning a court case for poor workmanship that they would be able to share so we can learn any lessons from the experience?
You need an independent assessment of the works. And one that will stand up in a court of law.