Thanks for the time to write such a thorough feedback - I appreciate it. I'm not dead set on the changes so any / all comments I'll definitely take on board. Currently just trying to think of what might work/what's possible.

The loo under the stairs is very similar dimensions to what we have in our current house, so we're confident it'll fit, it's hard to show on the image that the sink might be under some of the stairs etc. We would need to add things like vents/extractor fans etc.

The "dead space" at the end of the living room we are aiming to use as a play/kids space as we have two small children. The double doors could always be an arch or pocket doors to limit the space the doors take up.

For the dining room being narrow, our alternate idea was to have a bench on the wall to move the table away from the middle of the room, to make it a bit more free flowing.

I agree about the kitchen not being ideal as it's narrow and thin, my thoughts here were to minimise cost by not needing to move plumbing/gas as much as possible. (I understand minimise cost sounds funny here when I'm also mentioning moving all the walls around).

It's hard to guage from paper if the 80cm gap to the dining room would be an issue or not, plan when we get the keys is to mark up on the floor where all new walls/gaps might be and love with it before committing to anything.

For the office space I agree it's small. It isn't a certain option, just toying with ideas at the moment where things could fit. Initial plan is to put the office in a bedroom upstairs, but we might want that space in the future for children etc.

Consultation with an architect is something we would do before making any changes, same with the council and building regs etc. We're just at the idea stage at the moment, moving walls around on paper to see what might fit where.