In the short term, foreigners working in the UK do not take jobs away from citizens. They do jobs that are so arduous, and so low-paid, that citizens won't take them.

In the long term, however, the reason industry is organized around making those jobs exploitative is that there is a ready supply of foreign workers to exploit. If that were changed, British workers and these businesses would converge on treating workers better.

This alone won't cure poverty. Achieving that will require taxing the rich a lot more and ending their subsidies.