gosub
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Its a whole can of worms within itself. Wen, Chinese wife of a mate of mine, did some work at one of thosee Chinese medicine places - found the staff to be completely exploited, with the hold over them being :don't like it we'll cancel your visa and get someone else over who won't complain...I would say so.
Granting permissions (i.e setting restrictions via visas/ green cards etc) is a bit different than implementing freedom of movement.
Its not a trivial difference and if pointing it out us splitting hairs then any discussion on brexit is pointless, seeing as it's one of the key negotiation factors.