Probably better to ask ourselves more holistically what good urban design looks like.
There are very pleasant and extremely livable high density cities (or areas within them) as well as many example of lower density urban and suburban environments that are awful.
Also, buildings are not really getting “ever denser and taller” except in the most extreme cases. In London, for example we’re usually talking about taking low density low quality housing or currently unused or underused ex-industrial land and turning it into higher density housing, offices, and retail. But this is not so high density that it icomes close to pushing the boundaries of what’s already known to be workable, especially when paired (as it usually is in London at least) with public space, local amenities, and transport upgrades.
I agree there’s almost certainly a maximum density above which we don’t know how to make cities livable.
London is nowhere near that. The relatively dense parts that suck to live in suck for other reasons or because of poor design (read: lack of care for the people who will live there from the designers/funders). Sprawl scales as badly, though it’s easier to pretend it doesn’t.
As for the rest of the UK: there’s even more opportunity to introduce well thought out density alongside infrastructure improvements and create a net benefit for everyone.
> we're creating the problem by literally importing people.
This is the opposite of how I see it. The UK could easily grow by properly investing in cities and infrastructure without eating into green space (and still meet climate goals).
Given the current unsettled world, we should be opening the doors to the smart and ambitious with a sensible but significant plan to increase population and have multiple globally important cities in say 20 years. Check out Canada for an (albeit incomplete and not without its challenges) example.
