[ben_w]

> France also has four times the land area compared to the UK.

This is not by itself of great importance.

There's several different meanings of "built on", but even with the most expansive definition for this purpose, the UK could double how much is "built on" at a cost of around a tenth of what isn't: https://fullfact.org/economy/has-92-country-not-been-built/

There's other reasons to say "perhaps not a good idea" to a higher population (food security, energy security), but the land is there for more (or simply bigger) housing.

[tonyedgecombe]

That land use has to compete with other uses such as agriculture, leisure and wildlife so the smaller available area is important if you want to make that sort of comparison.

[ben_w]

Everything has to compete with everything, but:

(1) agriculture is both the biggest user and not done in a way that comes even close to maximising land efficiency; nor is there any reason it should, given there's not much pressure on agricultural land and the UK has easy access to cheap food imports.

(Even if there was pressure on farmland due to a loss of trade, it would be access to fertiliser that would cause more long-term issues than the land itself; phosphorus shortages would reduce carrying capacity in the range of 9-39 million depending who I ask).

(2) even with the UK's right to roam legislation, leisure use of most land is close to a rounding error. I mean, think about it for a moment: unless you live somewhere like Cambridge where the cows roam in the middle of the city, how often do you go to the middle of a cow pasture for a picnic? Ever tried taking a shortcut through a field of sunflowers (I did as a teenager, I don't recommend it)?

That said, on (2), UK land dedicated specifically to golf courses is close to (a little smaller than) UK land dedicated to housing: https://www.bbc.co.uk/news/uk-41901297