Another update:
It seems that, despite what I was lead to believe by the person I'm dealing with at Wickes, the company who did the job have to be given a chance to put the mess right, To that end, the two guys who own the company came to view the scene of the crime today. The reaction of the older of the two, obviously an old pro with many years of experience, was actually very reasuring. He was as horrified as we were at the mess and he wants to get a tiler with 30 years experience in to redo the majority of the wall tiling. He's worried by the floor tiling, though. He said that if he'd realised that the floor tiles were cork, not ceramic, he'd have turned down that part of the job, as they have no expertise in that area. That in itself was good to hear as it's not the kind of thing you hear cowboys say! He says that he's going to have to find someone with experience of laying cork tiles to take on that part of the job. I said that I'd ask if there was one on here and I'll be posting a message to that end in the relevant forum.
The ceramic tiling will be redone immediately after Christmas and the floor tiling as soon in the new year as someone with the relevant expertise can be found. As requested, photos of the finished work will be forthcoming.
Many, many thanks, once again, for all of your comments. You've helped us feel much more confident in sticking to our guns when the initial reactions we were getting to our complaints were pretty negative.