Thanks Dan,
To be fair, we did employ a highly recommended bathroom installer, who has excellent references. They have completed one bathroom in a porcelain tile to a really good standard, but for some reason the second bathroom with the ceramic tile hasn't worked out well at all in either the grouting or the cutting of the tiles. I want to resolve this with them fairly, which is why I have asked the question, because they are insistently and persistently telling me that you cannot get a non jagged edge on cutting a ceramic tile, whilst I can accept you might not get a perfect smooth cut, I just can't accept it should look like this.
I wouldn't accept that either.
But check this out. When people come on here saying "I employed a highly recommended builder", I've given up laughing. There's no such trade as a builder. A builder is the firm that employs the trades. So a bricklayer, plasterer, plumber, carpenter, electrician, etc etc - All recognised trades by city and guilds and you can get NVQ's in all of those trades.
Bathroom fitting, like building, isn't a trade.
To have a qualified bathroom fitter, you wanted to see City and Guild certificates for Plumber (water not gas) and Tiling. And if you needed stoodwork doing, perhaps plasterer / renderer or some other trade that covers it.
So the fact you checked references for a 'bathroom fitter' in its self means you could have only seen a business card with it on, and it perhaps says it in his name.
The proof is in the pudding. He's not a tiler. That's for sure.
We can bang on all day. The solution is above. Get tiles cut properly, and they'll fit perfectly, because the trim is perfectly flat/level/plumb (hopefully). Don't leave much of a grout line, and grout between the trim and tile, but you want about 1mm really for it to look nice. Although BS5389 stipulates 2mm. I just wouldn't go with that, because you have a light tile and dark grout. Again, something a tiler wouldn't have warned you about. But a bathroom fitter knows jack about.