Does the chimney breast not go all the way up?, because the plans don't quite line up. Another consideration is are you able to move plumbing and drainage to the opposite side of the house, and regardless of budget, wanting to deal with that kind of upheaval? Of course, the obvious thing is to make the ground floor extension into one room, but I think little adjustments like lining up the inner entrance hall and opening that up would be a minimal approach to making a big difference. Here is my pop at it, but trying to not move services too far or move supporting points (of course still needs new larger lintels or more, but basically in the same places). I just moved living areas to places that the natural light already serves... and no dark corridors added.

If you've got a family room I might be tempted to put a tv in there, use the dining room as a snug and have a table and chairs with a small sofa in the living room. Alternatively use the family room as your main living room and the dining room as play room (depending on age of child/ren). The proposed layout doesn't allow for much seating and also blocks the path from the kitchen and seems quite close to the stools. I think just seeing half of the back of the sofa may also look slightly odd?

Thank-you very much for the comments. I hope it will be a great space, but playing around with it and changing the design at the last minute is getting a bit stressful! This is the design that the build company showed us initially - just their initial thought as it how it would look. I found feeling the area where they had positioned the fridge/freezer very tricky. We want a free-standing french larder style fridge and the doors and level of matching with the rest of the units didn't seem like a good fit. The support pillar for the steel that crosses the island in the attachment below has also been a real annoyance. It sticks out 23cm, so it can only really go through empty-ish cupboards. Clearly anything to the left of that steel is difficult to vent. On the design in my intitial post, I was intending to have a dropped ceiling element that stretched just beyond the steel. This would let me have a powerful extractor and exit the flew onto the flat room (hidden by the drop ceiling 'box'). I like the idea you describe of a full wall of units, then island, then table. I guess Jonathan's proposal is similar to that. While I love the efficiency of the "4 double door" hideaway I just don't like the aesthetic, so will need to think about something else. Bringing it back to what we need... Utility room: enough to stash the washing machine, store the vacuum cleaner and hang a few clothes. No need for a sink. Free Standing, 90cm wide fridge, nicely framed either by wall of kitchen units. Waist height oven with an additional "top oven / grill (broiler)" - so at least one full height column. Good size kitchen island with at least two seats. Approx 90cm induction hob, plus a gas domino hob. Powerful, externally venting extractor over hob. I'm relatively open to moving the kitchen/living area to wherever it works best. I'm also not desperate to have the hob on the island (but that would be nice). As far as I know, the builders haven't done anything that can't be easily adjusted at this stage - but I think that will change in a couple of days - and they are planning for the kitchen to be in the old part of the house. As for rooflights - I thought, perhaps wrongly, that it would be light enough with the big bifold doors. It is an east facing room, and the old room had some sliding paitio doors and it felt bright enough. So I have left roof lights out on the basis that - but I'm also concerned about noise. (Cheaper too!). The biggest window we can gave without incurring significantly more cost is 1800mm x 1000mm - I'm minded to be 2 or 3 of these in that middle section. Thanks!

Be careful with tv up on a wall if anyone has neck problems or arthritis as it can exacerbate symptoms. It is advised that the tv should be below the eye line.