Owning your own home

I think that is a bad example. London’s growth in the last 20 years is just a reversal of the decline over the preceding 40-50.

Yes, but, well, not quite. London's (the LCC area's, which was much smaller than the GLC/GLA area's) pre-war was about 8.5 million. Much of this was slums and living conditions for many were truly appalling. Slum conditions have, of course, never quite gone away, but it is certainly better today. I've read reams on London's population statistics and I have always come away with the impression that its population must be much higher than 9 million today, or whatever figure is current. A GLA planner I know told me a few years ago (pre-'Brexit') that the rate at which London's population was growing was greater than ever before, even in the late 19th/early 20th centuries. Also, in those days London was still the capital of the 'Empire', growing much faster than other cities, and today it is merely one of many fast-growing cities, with its growth rate dwarfed by the real population (though not necessarily power) metropolises of the world, some of which are x times larger than London.

I don't think it's a bad example of how quickly growth can happen, though. Governments have all the power to direct economic investment, and most do. It tends to be in over-centralised states like the UK of France where this goes wrong. I'm most familiar with the example of Germany, where you have 'structurally weak' regions, too, but where there are constant efforts to strengthen them. And German economic policy is far from ideal, obviously, especially with the disastrous and corrupt sell-out of East Germany, but it's still better than over here, although it has been losing ground over the last couple of decades.

There is also a need for speed, as, for instance, former manufacturing regions have been losing skills for a long time now and there will come a point when those will be much harder to re-establish.