Brother and I have mortgage: Is it possible for one party to remove themselves?

If only it were that simple. This would mean he is liable to tax as it's not the rent a room scheme then as he is not living there.

Well then to the brother who stays, the moved out brother stops paying to the mortgage and rents somewhere himself.
 
This is where I think the establishment needs to be pragmagtic and merciful and I think the taxman would be to be honest.
 
Well then to the brother who stays, the moved out brother stops paying to the mortgage and rents somewhere himself.

That would work for the brother who stays as then it would be the rent a room scheme. But for the brother who leaves, what about his portion of the mortgage? If he doesn't pay it and the brother who stays pays it then he is acquiring a greater 'share' of the property.