Thanks mate, the guy admits he is no tiler but he's just been tiling for a long time.
Update on the colour thing though, CTD have agreed with me that the tiles should be the same colour given the description on the site, so they are taking it up with their supplier and honouring a FOC replacement for a suitable tile. I'll head over this afternoon and try to find one which matches as close as damnit... also, point is taken on the mismatch tile widths, I can use the opportunity to try and find a 400 width tile (if those are a thing) and we can now line the grout lines through.
So big shout out to CTD who really came through in the end.