I should probably write a bot to auto-reply when someone pulls a state as a comparison.
(Or ask the resident flamingo nicely to write it 😀)

I'll put the gist of why hot weather can be a pain in the UK so it's in the thread, not aimed at you obviously:

• Most housing was built around coping with -5 to 25'c comfortably.
  Which for a long time meant no insulation, and a fire/wet central heating system.
  And not a damn was given about air-tightness.
• A lot of the housing pre-dates WW1
• Air conditioning was not commonplace at all when the majority of houses were built (you could argue it still isn't)
• Heatwaves were so infrequent, it wasn't worth the cost of installing air conditioning domestically.
• It gets muggy as hell, with the high humidity making it worse. (But again, it's variable, so tricky to justify spending money)
• Swamp coolers don't work due to the humidity
• Lots of people grew up with the weather being (generally) mild enough that opening a window to get airflow was enough to keep cool. (I've had family members open the windows on a 30' day to "cool" my 20' basement...)
• Leccy is expensive. This is improving with solar and plunge pricing, but most people will want to tighten up their house in other ways before spending £8/day cooling it.

With both our warming climate, and more kit being installed, things are changing, and people are adapting.
More people now understand that cooling the fabric of the house at night when it dips into the teens, then closing the windows in the morning, is a better way to keep it cool.
Building regulations stipulate significantly more insulation, air-tightness, heat gain control.
And air conditioning has dropped in price a lot.
For anyone curious, you can DIY a mini-split for about £500/room, or get a better quality one installed for under £2000.

I mean, retrofitting whole-house HVAC is a pain, but it's not hard to get a window unit.

We tend to want a 240V heavy appliance outlet for beefier window air conditioners, but you've already got that as standard on British household circuits.

EDIT: Hmm. This says that the British convention is swinging windows, which aren't as amenable to window units, and one should get a (slightly noisier and less efficient) portable unit instead of a window unit. But basically, same idea. I'd get a unit with dual hoses; doesn't cost much more, more efficient.