I listened to an excellent Radio 4 program yesterday on the topic of "slave" doctors being recruited by private companies from Nigeria to work in private hospitals. There is a BBC report here
https://www.bbc.co.uk/news/uk-63141929
Not only do these private firms target countries which are banned from recruitment, due to their own country needing them, but they work them up to 3 weeks on (24 hour on call) and deduct pay if they can't work due to tiredness, are ill or need to take time for management, appraisals and admin. They all end up working for private hospitals, like Nuffield Health under conditions that the NHS do not allow.
If they moan they get their visas cancelled. Literally treating them like slaves.