You’re assuming they want to work here legally, they don’t.
That is one of the great unknowns. I have been reading up as best I can. There is limited research, but it shows that benefits are not a driver of illegal migration. That makes sense to me. People don't travel thousands of miles in terrible conditions, risking their lives, in order to claim benefits. These will mostly be people with drive and grit who want to better themselves through hard work. Like most immigrants have for hundreds of years.

