You also have to be an MP.
Currently Kier Starmer is a Labour mp in an area of London. He’s resigning and is being replaced by someone (Burnham) who was Labour Mayor for Manchester, but stood as MP in an area of Manchester last month after another Labour MP resigned.
Burnham beat reform in that election, and Count Binface. There was a discussion thy given how unpopular Labour is, that reform might win. In the end everyone who was anti reform (Farage’s party) voted Burnham and he got 55% of the vote.
While the sentiment in the U.K. is that if a general election were held tomorrow, Farage would win his seat, and reform would win a large number of votes. In reality polling puts Farage’s party around 25%, with four other parties on 10-20%. As the election isn’t proportional though it’s possible reform could get 55% of the seats with 25% of the vote, however last time they got 1% of the seats with 12% of the votes.
I don't think that's strictly true. You definitely don't have to be an MP in order to hold a cabinet office. I think that extends to the PM as well. It's never been tried obviously.
The last member of the House of Lords to be PM was Lord Salisbury in 1900.
As noted Alec Douglas-Hume had to leave the House of Lords in 1963 and get elected as a MP.
The previous attempt would have been Lord Halifax in 1940 but by then it was clear the PM had to be from the Commons.
Firstly, that election is three years away; it's a separate political event.
Secondly, that depends on the outcome of at least three hundred constituency elections, which would have to return Reform candidates. They did OK for a minor party at the last council elections, but they have a very high attrition rate as candidates are discovered to be above the acceptable racism threshold, bent, mad, or simply never intended to do the job in the first place.
A Lord can’t address the commons, which was most recently an issue when ex PM David Cameron was made foreign secretary in the dying days of the last Tory governemt.
There have been non-MP (ie non-Commons) PMs.
I suppose that in theory if Reform could form a government after the next election, but Farage still didn't get a seat, a party colleague could become PM and appoint him as a peer. There's a rich history of politicians losing elections and getting appointed this way instead, though as far as I know none of them subsequently became PM.