Pity you have decided against glass in favour of tiles. We have just done our kitchen and I wanted an easy-to-clean surface for the splash back, so the rough surface of grouting around tiles, and also the indentations on some patterned tiles (which collect grease and grime) ruled them out for me! I went for glass, which the manufacturers matched exactly to the duck egg paint colour on the other walls (just gave them a product code of the paint), and although the initial outlay for the glass was expensive, the surface is so brilliant to keep clean and it looks fab as well. I would definitely recommend, and you could match it to, say, your lovely pink/purple ceiling lights ...

Hi Irina! That's a really lovely kitchen, I think perhaps using a natural material with variation will be an excellent finishing touch...have a look at our New York Brick tiles, we keep these in stock in West London can send a sample if you think these could work http://www.stoneandceramicwarehouse.co.uk/wall-tiles/floors/item/new-york-bricks

Hi! Not keen on metro tiles to be honest although the narrower vertical ones aren't as bad 🙈 Just thought of a nice shaped one but struggling to know what colour works with a marble worktop 😂

Yes, you're correct, if you have your splashback up against the extractor then you'll trap the back of the hood facia, which you need to be removable for access to the grease and carbon [if fitted] filters. TBH the worktop guys would just template up to the extractor, they're not kitchen fitters and they're doing what they've been asked to do. Not having an extractor where you previously had an extractor, as a rule of thumb, shouldn't be done under part F of regs, for good design practice you don't make the extraction worse and if Howdens have designed and supplied this then its not suitable. If you've outsourced the quartz could be a bit different though. Howdens do have deeper wall units at 390mm.