This. London can't grow much more - it can densify up to a point, but you can't build much more on the edges of town without some enormously expensive infrastructure upgrades through the middle. Which they should probably do anyway, a tube line, a Crossrail line and a new HS line every decade or so, but neither Labour nor Tories are into that politically, because of London-envy in the rest of the country.

Manchester, Birmingham, Newcastle and the larger university cities on the other hand, masses of scope, and on a much smaller budget and shorter timescale.