Who exactly are we supposed to "rhrow out of the country"?

If some people are wanting to throw ou 'non-brits' then how exactly do we decide who can stay? Can my son stay seeing that his grandfather is jamaican and may have a slightly darker complexion to your average klu klux klan member? Or even his mothe (my missus) as she is half jamaican and must strike the fear of god into any racephobic people she meets