Population chart of London, but it has happened many times in history.
City-based booms bring people in, eg financialization era since mid-80s or Victorian empire/ industrialization, but living costs rise and then when the growth is outside the gateway city, eg if manufacturing grows in the Fourth Turning/ post-Brexit, people leave the high-cost city.
If over 30 years the population shrinks, it will turn forecasts and value of 'core' assets on their heads
These cycles can last 3, 4, 5 decades typically. London's current growth cycle is over 3 decades old.
London I have said before is functionally bankrupt. It's too expensive for regular people to live in and have a decent quality of life.
Anecdotally I know many people moving elsewhere in the UK or going back to home countries. Corbyn is obviously going to win the next election and many of his policies will speed this process up. He will help manufacturing and services you can work remotely for anyway.
In the States there is clear evidence of migration away from high tax, high cost coastal gateway cities.
The one exception to this I would expect is Hong Kong, where you have all of these same cost of livign issues, but next door there are 1billion+ people in a dictatorship, so Hong Kong real estate can deflate but I think the population numbers should be stable or even grow.