Whatever the merits of the idea, there's a very odd statement from shadow home secretary Chris Grayling.
"We envisage the Mayor of London being the elected police commissioner."Now this could mean that they expect the current Mayor of London (Boris Johnson) to also run for the post of police commissioner, and just happen to win. But it doesn't mean that.
It might even mean that they expect the Mayor of London to be the temporary holder of the police commissioner role until an election can be held - though it would be a very strange way to say it. But it doesn't mean that, either.
What it means is that the Mayor of London has at some point in the past been elected; and that he will become police commissioner by virtue of his position.
I don't really think that is what anyone thinks they meant by "elected police commissioner". Do you?