My advice to "millenials" (well I think technically I'm one, so let's say younger ones) is to stay the hell away from London. I read these articles on the housing crisis and staggering rent amounts and wonder am I even living in the same country as these people.
This basically amounts to advising them not to live in a city (which is fine). But some people do like living in cities, and London is really the only option in the UK if you want to do that. No other city in the UK is anywhere close to London in terms of culture and economic opportunity. Yes, rents in Manchester and Birmingham are lower. But you're going to get paid less, you have to live in a second tier city, and…
Also the idea that other cities are second-tier is incredibly biased. Sure London has some things that the RUK doesn't but there are also plenty of things you can't get in London (fresh air for one). It's a different lifestyle, not a 'second tier' lifestyle. Also other cities are cities, they might not be mega cities but that's not the definition of the word.
Lastly the career opportunities part depends. Yes there are less opportunities but there are also far less people vying for them. Smaller pond but bigger fish. If you're a careerist looking to become the top 1%, London is probably your best bet in the UK, but it's perfectly possible to work in the top 10% outside of London.