in reality, the UK isn't poorer than before. It is about the same - no growth. It is only poorer when compared to the US's growth.
One's labour, when being paid market rates, does not make one's country poorer. And those profits from said labour was paid for by the acquitition of the capital - money was invested.
So in essense, the "poorness" that the UK feels right now is not a result of these companies getting foreign ownership, but the UK gov't lack of industrial policy and investment. Brexit is the last straw probably.
That's a weird conclusion to draw.
Governments aren't generally known for their ability to pick winners ahead of time. How about instead of trying industrial policy (again), the UK could try to remove roadblocks that keep them from having successful companies?
They could also try to leave more money in the hands of taxpayers, so they can invest.
Rich foreigners are happy to invest in the UK. See eg Deepmind itself, which was bought by Google.
> [...] so our labour enriches other countries while our country gets poorer.
Foreign investment is usually seen as a good thing. Especially foreign direct investment.
And: why do you care so much what passports these rich people hold?