@catalanqueen it has struggled but it's still alive! It has been in a few rooms around the house, including the bathroom which it didn't seem to like - despite having a large window I think that the spot it was in in there was too dark for it. I've recently moved it out to our sunroom, where it seems to be thriving (contrary to all of the recommended growing conditions for calathea). The humidity is low but I've found that wetting the leaves at least once a week keeps it happy and it's throwing out lots of new leaves which is great.

If you really can’t face applying for permissions then get someone else to do it for you. This is one of the services an architect can do for you. As far as where you extend I think a side return makes the former dining room less light and less useable but people accept this as they are protecting often modest gardens. If your garden is sizeable I say have an internal courtyard to help bring light into the centre of your house as you don’t have to be as economical with the garden.

As usual the Houzzers are coming up with fabulous ideas. I just love this site! My little suggestion would be to add a feature standard lamp in the dining area, perhaps a wooden tripod one with a material shade? Houzz have several on their product listings but here is what I mean: https://www.houzz.co.uk/products/romanza-tripod-floor-lamp-white-prvw-vr~127702569 I would also suggest bench seating for the dining area rather than chairs as it keeps the clean look. This is quite expensive but would work nicely with your table I think. https://www.houzz.co.uk/products/z-kollektion-bench-small-prvw-vr~110078871

What a huge room! Guessing you have a big family and need all the chairs on a regular basis? What was the original intention with the artificial living wall? Is it just artificial grass or do you intend to add to it in some way? I've never seen one before so not sure if that's the finished article. Aside from that, I think it's tricky with a really large table and lots of chairs, for it not to have a bit of a "boardroom" feel, so I'd be adding things that make it feel really homely. Some ideas: paint the walls a darker colour (at the moment all the colours are very similar and pale, I think some contrast would be good). A large room with a light floor and tabletop like that can probably take something quite dark - eg an aubergine or navy. Or if you want to stay neutral, look at some strong greige or beige tones (not grey which will continue the cold feel). Or something like a dusky pink might work with the chairs. Or a light terracotta. I would also put down a large rug if you can source one that's big enough to sit under all the chair legs. And bring in some real plants - a lovely big Monstera or something, in a planter made from natural materials (eg a big basket). Art on the walls - choose something you love and that means something to your family, not something that might be chosen in an office block. And while I'm usually a fan of clear surfaces, I think I'd be putting something on the tabletop itself, for example some candles in glass lanterns, pots of succulents, that kind of thing. Keep all the materials natural (eg cane/wicker, terracotta pots, glass lanterns, linen if you want a table runner, etc) and avoid anything faux, plastic or shiny which will just add to the "hard" feel (perhaps just a small amount of copper/brass to pick up on the light fittings). Check out Neptune's website and social media accounts for ideas - they're very good at creating cosy spaces with a well chosen display of bits and pieces.