However, conventionally the Prime Minister will be chosen from the ranks of elected Members of the Commons, and all the Great Officers (the senior cabinet posts like Foreign Secretary or Chancellor) will likewise be MPs. So every Prime Minister in living memory was the elected MP for their constituents.
Since it's only a convention the Commons certainly could just decide not to do this, and of course there isn't anybody to stop them - but that would be extraordinary. It hasn't happened at all in the modern era.
I guess the most plausible way it could arise now is if there isn't any majority in the Commons after an election, a conventional senior-junior coalition partnership in which the larger party gets PM but the smaller party gets some other roles is impossible for some reason, and the "obvious" compromise centrist politician has meanwhile been elevated to the Lords.
Nothing in the existing rules actually forbids a Lord being PM, it would just be incredibly inconvenient (the Commons hold the PM to account not the Lords so...) and look undemocratic, so I guess in that case they might decide the way forward is we put this chap in place as caretaker, his executive gets us out of whatever immediate hole we're in, and then hold fresh elections. If there is a decent majority in the Commons for that idea, it's enough to make it happen.
Since it's only a convention the Commons certainly could just decide not to do this, and of course there isn't anybody to stop them - but that would be extraordinary. It hasn't happened at all in the modern era.
I guess the most plausible way it could arise now is if there isn't any majority in the Commons after an election, a conventional senior-junior coalition partnership in which the larger party gets PM but the smaller party gets some other roles is impossible for some reason, and the "obvious" compromise centrist politician has meanwhile been elevated to the Lords.
Nothing in the existing rules actually forbids a Lord being PM, it would just be incredibly inconvenient (the Commons hold the PM to account not the Lords so...) and look undemocratic, so I guess in that case they might decide the way forward is we put this chap in place as caretaker, his executive gets us out of whatever immediate hole we're in, and then hold fresh elections. If there is a decent majority in the Commons for that idea, it's enough to make it happen.