((Assuming your not joking.))
Its a thing in Parliamentary democracies...
They may be Monarchical or Presidential or run by a collective committee... (nah)
The Prime Minister is chosen by his/her Party (though even that is not required) and that choice is validated (if only by convention) by Parliament when the PM forms the UK Sovereigns Government in the common/reps . They are simply the Prime Minister among other Ministers.
The *Electorate* do not vote for the PM they vote for their local representative.