Unlike the US, where there is a strong sense of turn taking and unsuccessful candidates from previous election cycles frequently and successfully run again (Biden, H Clinton, McCain, Romney, Gore, Bush Snr etc), successful second attempts are *really* rare in the U.K.
In fact, across the two major parties since 1964, there are only 2 examples of successful 2nd time around runs. Only one of these made it to be PM.
First, let’s look at a list of Conservative leaders: Johnson, May, Cameron, Howard, IDS, Hague, Major, Thatcher, Heath.
Of these, Michael Howard is the only 2nd time round candidate, having run in 1997 and again in 2003.
Unusually, an honourable mention goes to Boris Johnson here too, as he started to organise a run in 2016, but then announced he would not enter the contest after Michael Gove (supposedly a supporter of Johnson’s) launched his own campaign. He won in 2019.
Now let’s look at Labour’s leaders back to 1964: Starmer, Corbyn, Miliband, Brown, Blair, Smith, Kinnock, Foot, Callaghan and Wilson.
Of these, only Callaghan ran twice, finishing third in 1964 when Wilson won, and then winning in 1976.
So this would suggest there aren’t many second acts in the major parties for would-be leadership contenders.
(This thread is largely put together from memory, so happy to be corrected if I missed anything glaring).