MVHR makes total sense and sounds superior. I’m sure the builders have successfully lobbied against such a sensible suggestion for decades and that’s why we have (I imagine) such stupid and basic solutions in our building regulations.
I feel like UK houses lack infrastructure that the likes of the US and Europe have. Even kitchen ventilation is such an afterthought
1) huge thickness thermal insulation on the exterior
2) double/triple gaze (airtight minus the small built-in ventilations) windows
3) NO added mechanical ventilation
The bets are on on how long it will take for people to realize that if they do not vent manually the house humidity/mould will form.
This has already happened for houses built some 10-15 years ago (the first houses built as Class A or Class B) that - even if newly built - did not usually provide mechanical ventilation.
There are on the market since a few years small "in-pipe" mechanical ventilators, including a heat exchanger, basically you make a 100 or 120 mm hole in the wall and put in it a pipe that contains the vent and heat exchanger, they are very suitable to install "as an afterthought".
Trouble is that they work on "alternate cycle", i.e. they suck air from the inside for - say - 30 seconds (warming the heat exchanger), then they push air from the outside for another 30 seconds, and they may be (or become) noisy, new models have built-on timers to be able (as an example) to switch off at night if in bedrooms or switch off in the evening in the living room, etc.
However, getting that ventilation using trickle vents in windows is just a stupid way to do it. You're letting all the heat vent out, and letting the noise in. A better way is with a mechanical ventilation heat recovery (MVHR) system. That sucks air out of some rooms (the bathroom and kitchen are recommended), and passes it through a heat exchanger before pushing it outside, while simultaneously pulling in fresh air from outside, heating it up in the heat exchanger (for free) and blowing it into other rooms (such as bedrooms and the lounge). This is the proper way to do it.
A MVHR system only really makes sense if your house is otherwise fairly non-leaky. However, if you do install it, then it can take over the bathroom and kitchen extraction, and it allows you to plug all those leaks and insulate well, without causing stale air problems.