During my last London trip, I had the impression that they mostly employ young people from all over Europe. I suspect they will all be gone end of year.
That aside, if someone is here under freedom of movement that doesn't mean they qualify for a work visa, surely? No low-skill jobs would meet the income threshold needed to get a visa?
https://www.london.gov.uk/what-we-do/eu-londoners-hub/settle...