What can I do?

[nostress]

Builder totally messed up the tiling (they undulate and are not flat so there are shadows from some of the higher tiles) and has overun by nearly two weeks. He cant make it right without ripping out all the tiles and starting again and thats not going to happen. Just really disappointed. His excuse is big tiles/uneven walls (but they had been previously scimmed).

Contact trading standards for advice, they might be able to help. Please don't pay them. Got ripped of for a huge amount of money by dodgy builders.
The tiles will have to come off though, but don't allow him to do it. The tiler should have dragged a big spirit level or something over the surface first to see if the walls ran true, as often they don't.