There is another slant to this whole thing that I think you should consider. Perhaps this person is not only your friend, but in his eyes, you are his BEST friend, and all the things he has done and is doing is a hugh cry for help. Don't be afraid to have him placed somewhere (wherever UK has that can provide the help) even if it takes an arrest to get him there. Remember that sometimes what appears to be the cruelest thing in the world is actually the best.
Not an easy one! My best to you, and my support in whatever you choose.