Nice house. Mailman got the main ones, so I follow with extra works with constraint that the money spent has to eventually more than pay off. You can say "gosh we'll have to save up for ages first" to which I reply that I hope you can.
i) inside front and rear exterior-facing walls, next time major redecorating such as full strip and wallpaper, and possibly major rewiring the ring mains for 3-pin plugs,
consider fitting serious extra thermal insulation panels. For example, losing two inches off room internal dimensions, you can add 2 inches of really good insulating slab, which you paint over.
ii) This suggestion was removed because it encourages doomsday preppers and people like that.
iii) secondary glazing winter warmer inside the bay windows. I'm evaluating 10mm twinwall polycarbonate which so far I like. I mainly use the cheapest possible way to get triple-glazed thermal performance, which is to have screwed together removable wooden frames to fit loosely on inside window sills, painted them white, and taped on cling-film. Passes light but too crinkly to see clearly who is outside; comparably to net curtains which should probably be re-hung to hide this DIY monstrosity. Cost me about 3 pounds per window. Blocks opening that window for the duration of the winter heating season. Presently half of my windows have it up, and the other half get opened too often for ventilation.
iv) The council planning department might say a few things about this. Your house has a big surface area of side wall losing heat, and so does your neighbour in the picture. One really big change would be to insert a mid-terraced new house in between yours and theirs, replacing your garage and filling in their side path. Have a look at terraced house sizes next time you are somewhere. Mine is 4.2 metres width. After you've sold the extra middle house, you've just modernised from being a semi with bay windows in a leafy suburb, with big exterior surface per occupant, to being house two in a block of five. This presents many advantages for the new occupants of being inside walking and cycling distance of all the nice things in your leafy suburb, and for you and the other semi in the photo, you get as much heat back through the side wall as you leak out.
v) plant some fast growing hedge or trees and consider fly-planting trees on any disused land in your neighbourhood which you are willing to coppice stack and dry in your garden. Anything which grows from what you plant is genuine nil-net-CO2 if you can burn it in your fireplace.
vi) get your chimney swept and inspected, and find out what is allowed in your existing fireplace. Newspaper from here gets put in a recycling bin, then driven 82 miles to a presort works, where it is mostly discarded and dumped to the incinerator next door. Would using your newspaper at home to start your fireplace from time to time be no worse ?
v) inside your blue front door and wide hallway with side windows, put up a full width full length curtain,to be drawn after dark.
Lastly, be sceptical about certificates and tick-box inspections. Planting more trees for firewood won't change your certificate rating, but do that anyway if you think that it is right.