love this fireplace. A mantel would really distract from its elegance. Yes, absolutely do not let the painting rest on the surround. the width of the one already there is better proportioned than the one on the left. the desk is beautiful but needs to echo the fireplace by placing a taller lamp on its left, where the poinsetta is. Drop the painting above it, lower, & gradually add two more paintings above, (just play!) so you have 3 which will echo the line of the fireplace. The arrangement within the fireplace needs to reference the lovely stone & I would find a simple large glass jar & fill with tall cow parsley, grasses or anything country & natural in season. Tall lilies if you must. Do not forget the power & softness of foliage... Go for a walk & find an interesting piece of bark or stone to put to the left of the tall Glass jar or both to sustain the always decorate in 3's rule! (Find some greenery while you are at it!). Above all do not ruin the simple beauty of your room..I envy you your fireplace, a few easy tweeks & you are there!! you could do it today!

Tall units up to the ceiling can look very nice, although would function as displays mostly. Honestly standard height kitchen wall units wouldn't concern me, they might accentuate the height which is not a bad thing at all. Alternatively if you have enough storage in the base units why not skip wall units altogether? Open shelves or even nothing, just a stunning splashback

I think this looks great. Could I please ask is the ceiling brilliant white? In my experience decorators are a bit old school about ceilings and radiators being bright white but in my opinion painting the radiator in Dix Blue would make it disappear. In my opinion the slightly vintage feel of Dix blue is better suited with a soft or aged white- I like Cornforth White for its grey quality which in my opinion only looks grey when contrasted against brilliant white but would soften the look in this room.

I agree with above - you're going to have a lovely bright utility! The usual way people extend is to put the utility and WC into the darkest bit (turning the utility 90 degrees like suggested above) which then pushes the kitchen/dining/living towards the garden end. But that would have involved more walls coming down - I feel like this is a case of you got what you asked for, but now you're asking for something else. I think the architect has come up with the best layout though for minimal work involved - putting the dining table in the dark space will just make it a corridor and you'll mostly eat at the island in the light room with garden views (other than dark evenings like you say when being in dark dining room will be quite cosy). I know people who have done that and regretted it and wished they'd put the kitchen in the dark bit as you tend to be doing something in there anyway and you'll be looking through the lovely bright space rather than being in it. Getting a decent second living space seems important to you so the current layout achieves that. You could perhaps add some high level transom windows between kitchen and utility to bring more light into kitchen (depending on where tall/wall kitchen cabinets are going to be and how ceiling is). Another option that you haven't mentioned is to put the new lounge into the dark space (then you'd have to call it a snug!). Leaving the new space as kitchen and dining. But perhaps you want the sofas to be looking onto garden, or you don't want it right next to the other sitting room - which is understandable. So it depends on what you'd use that living space for - or would also having a couple of upholstered chairs or a window seat in the extension allow you the flexibility you are looking for? Regarding the loo situation - I don't like having to walk through the utility to get to it (mainly as you're going to have to clean/tidy your utility every time guests come round, no thanks) - alternative is to walk through the WC to get to utility - would result in a bigger WC (you don't want to squeeze between toilet and basin so put them on the same wall) and a more useful utility space - and you'll have one window into WC and one into utility and nobody will be walking through the cat litter tray - could keep the pocket door idea so that it's more like one room normally, but easy to close off the messy utility when guests arrive (if that is ever allowed to happen again!)