Thanks everyone for your replies.
It's a pity about the ply thickness but I think it's too late to do anything about it now.
I will be insisting on replacing those tiles which are giving giving a lippage of 1mm (probably replacing 4 or 5 tiles) and will then have to live with the result...
That's a pity, I was assured before the work started that ply was the way to go. Guess it's too late to do anything about that.
Thanks - another new word for me, and at least I can refer sensibly to the problem now.
The tiles are 600 x 300
As part of a complete new kitchen I have just had the floor tiled professionally. Before laying the tiles the floor was covered with 6mm marine ply so the tiler was starting from a flat surface.
The tiler is on holiday this week but when he returns I will get him to replace at least four...