"To build up London solidly from Brighton to Northampton (which you appear to hanker after)"

This old non-argument against whatever-the-person-saying-it-wants-it-to-be-an-argument-against was thrown at me recently.

I have never suggested this, of course, and anybody with a grasp of numbers would know that no sane person would seriously suggest this.

Why?

Distance from Northampton to Brighton approx. 125 miles.

A circular city with a radius of 125 miles has a surface area of 13,000 sq miles, if we adopted the Scandinavian "green fingers" model and put aside one-third of that for open spaces and built up the rest to the same population density as Greater London, there'd be space for 120 million people.

That's twice the current UK population, not all of whom would want to live there anyway*, so there would simply be no demand. Whoever tried this would soon go bankrupt.

* In economic and environmental terms, and with the benefit of hindsight, it would have been better for us to build and live in huge cities of tens of millions of people instead of being so sparsely scattered over large areas, but it didn't work out that way for historical reasons.