Can a mental condition prevent one from immigrating?

Hi there!
I read that a person with a mental illness and a history of a harmful behavior associated with the illness would be grounds to deny a greencard.
So, I was wondering: is there a similar policy in the UK? If so, does it also apply to people immigrating through family unification? (marriage and the like)


Thanks.

Possibly yes (320(7), 321(iii)).


regards