The UK has a ton of old dwellings. Like, a three century old home isn't even a local landmark. It's just a house.

They have of course been retrofitted with electricity and plumbing and gas and modern insulation (usually), but exactly what you get depends on how recently it's been renovated. And "mid 20th century" is a very common answer.

Not really, the U.K. has some of the oldest housing stock in the world. For e.g. my house is pretty typical, built in 1912, it has a double skin wall of bricks but with no cavity. It has three original fireplaces which are all very draughty. I have timber sash windows, and though I recently got double glazing my neighbours on either side do not have it.

Buy a "chimney sheep". Made a huge difference to me.

I had a look at their home town on google maps, and it looked like 1/2 to 1/3 of the town was still made up of old terrace houses. I imagine it would be tricky to selectively demolish them.