I think remove wall between kitchen and dining room. Add a utility room to the garden room and also possibly add doors out to garden on left. I've done a very rough example to illustrate.

It depends on your budget. There are so many options. You could extend and fill in the corner. If you did this I would move the kitchen in there as it naturally leads onto the dining. Kitchen becomes utility. Sitting room becomes family room/hangout space and the front lounge is for occasional use. If you did this you could have a skylight or two over the kitchen and larger sliding/bifold/crittal doors out to the garden. It may be cheaper to extend than start removing structural walls.

Thanks so much for these ideas! All different and have good selling points. Particularly interested in squaring up the back by extending back since the shadow cast by the back reception room renders that bit of the garden pretty unusable.

Does a garage and side access abut the WC ? if so do you use it just for storage?

Great house! Just be careful, if you do decide the square off the back, that you don't make the middle of the house dark.

Lovely space and a lot of options! After 4 renovations, and some of them with small children, this is what i would advise:

• squaring off the back is definitely a good idea but do consider extending further than that if you want a big space enough for a dining area, kitchen and sitting area/playroom, adding skylights and planning the spotlights/lighting according to where the skylights would be. You don’t want a skylight over your dining area while you could have lovely pendants over your dining table or kitchen peninsula.

• create a small utility and make the toilet accessible from it rather than from the open plan. Or even better, I would squeeze the toilet under the stairs. When you have guests, they would feel uncomfortable going to the bathroom if everyone is socialising in the open plan

• if you extend further out and the open plan is quite big, I would advise closing off the wall to keep the front room separate as a reception room for adults. If it’s all open, the kids take their toys and messiness everywhere and you wouldn’t want your velvet sofas smudged with Nutella and tomato sauce 😀

• you could also extend a bit on the side to make the utility which would free up more space for the open plan

The floor looks like nice real wood which you could keep unless it’s too cold in the winter. In our 1930 we had to rip off the floor boards and re-insulate underneath. Then we did underfloor heating. It is a considerable expense but if you’re planning to stay in this house for many years, it might be worth considering.
Finally I advise to always have a window ideally over the sink in addition to whatever door you go with whether a bifold, crittal, sliding or french door. It’s nicer to look out to the garden while you’re by the sink rather than a wall. This way you can also let fresh air in without a toddler jumping out into the garden if the only option available is a door.

I hope this helps and I wish you all the best in your project xx