My last house was a town house built in 2001. I bought a portable airconditioner for it in 2002 and it got used about four nights a year largely because the master bedroom overlooked a fairly busy road which often had drunk people walking home from the pub along it and sleeping with the windows open was problematic - the portable AC provided a much more tolerable form of noise.
We moved to another new build, detached, when we had DC1 in 2017 and it's like an oven. The sun used to stream in through the French doors of the kitchen diner at the back first thing, and then through the bay windows at the front all afternoon. Internal temperatures can jump from 23C to 31C in the space of a few hours simply from the solar gain, and with brilliant insulation shedding the heat overnight meant staying up with all the windows and doors open until well past midnight if it even cooled down.
Adding a conservatory at the back, over the French doors, paradoxically helped because while the air temperature in there can regularly exceed 50C the smart glass roof stops the worst solar gain.
The layout of the plot stops us planting anything to shade the windows. Although it would have meant replacing them all with inward opening ones I applied to the freeholder to fit external shutters, and was declined, and just for good measure the freeholder also declined my request to paint the red brick walls white. I grew up in the tropics on two different continents and know about passive colling measures, but very little works on this house thanks to the cunts at Peel Holdings..
We bought a second portable AC and then a third when DC2 came along but neither my wife nor the DCs were thrilled with the noise and they were a faff and not very effective.
Having installed solar panels and a 9.5kWh battery, we installed permanent AC last year and haven't looked back. If the kind of heat domes we've had twice this year already become normal - and the actual science says it will - I just don't see how much UK housing stock is going to be livable without AC.