Ted Heath famously refused to leave Parliament when he lost the Conservative Leadership election to Margaret Thatcher in 1975. Throughout Thatcher's premiership (1979 to 1990), he sat on the backbenches glowering at her in a "Great Sulk". He continued like that in John Major's premiership too, not retiring from parliament till 2001.
There are some who believe former Prime Ministers can be of help to the current PM, as only they know first hand the stresses of office.
But that only works if they offer constructive support. There is no evidence that Heath offered constructive support to either Thatcher or Major. Instead he seemed to stew with jealousy that they were in the top job and not him.
Poor Rishi Sunak started his premiership with three former Prime Ministers sitting on the backbenches, all seething in one way or another. It didn't help that he had to fix their mistakes.
Boris Johnson was visibly taken aback at the vast improvement the Windsor Framework was over the Northern Ireland Protocol. In the end he was one of the few MPs who voted against it, claiming it could have been better (even though the NI Protocol he had negotiated was a lemon).
Next up, Theresa May who is seething that Sunak has undone her madder policies. He's removed loopholes in her modern slavery act that allowed bogus asylum seekers to claim refugee status by pretending they are slaves.
He's also unpicking her Net Zero policies, which she had rushed through parliament without any idea of how much they cost or how the targets could be achieved.
As for Liz Truss, she's seething that the financial markets trust Sunak more than they did her.
All of this makes one appreciate David Cameron, who graciously resigned when he lost the 2016 referendum, and then left parliament shortly after, keeping a low profile and trying not to interfere. The only well behaved person in politics.