Tiler is off site today but the builder / project manager who built and tanked the shower area said he had noticed the irregular cuts yesterday and spoke to the tiler who apparently was following the former lines exactly.
However, this morning, contacting the shower tray company revealed that you can indeed go "off former" to meet the corners of the grate without any issues.
The problem now it that its all gone off and they say that it may damage the tanking, waterproofing and even the tray if we take out the 3 back tiles meaning the whole build will have to be restarted.
The dilemma we now face is - do we get them to redo it. The issue I suspect is more aesthetic but I just can't unsee it now and have to weigh that up against the cost of it all going wrong.
Incidentally I felt absolutely terrible mentioning it this morning as they have done an amazing job, but the devil really is in the detail and had to do it as with all the money invested in this, I really wanted it to be perfect!