Technically of course, however the monarch is "advised" by the previous prime minster, who by convention tells her the person who can command confidence the hou

Technically of course, however the monarch is "advised" by the previous prime minster, who by convention tells her the person who can command confidence the house, which is the person who will get 50%+1 of the votes. If we're being technical the PM does not have to be an elected MP, and can be from the house of lords.