S
smartv11
If Del is correct with his British Standards for lippage tolerances (I am not a pro tiler so cannot comment and would seek pro tilers confirmation on this) then you need to let us know how wide the grout joints on the floor are. The minimum grout width for a floor is 3mm.
If you're unhappy with the work, you need to try and resolve this with your builder by giving him the chance to address your concerns and rectify the situation. If your builder won't return to address your concerns, you need to put your concerns in writing to him. There is an independent body, TTA, who can independently assess the work that has been done by way of an inspection and report, but you're looking at a cost of around £700 for this. Alternatively, you could source a tiler who is unconnected with the job to come and assess your concerns and provide a report directly without having to involve the TTA and this could be done for a fee you agree directly with the tiler.
If you are unhappy with the work done and would like a second opinion as to whether your concerns should be taken seriously, this forum has a number of professional tilers based in Kent who may be able to give the job a look over with you.
Girlracer, could you please send the BS clause in full, as I've found BS5385, which offers different advice