Check your facts!
"The voting is split equally three ways between Labour MPs and the Labour MEPs, party members and members of affiliated trade unions who have not opted out of paying a political levy."
Reuters
I think you are confusing Leadership of the Labour Party with Prime Minister of the UK, they are not the same thing.
I care little in relation to whom is leader of what party and that is for each party under their own internal party rules to decide..
The issue I keep referring back to is HM's Prime Minister.