The Conservative party needs another leadership election right now like it needs a hole in the head. Most observers agree about this. Even Jacob Rees-Mogg accepts that four Tory leaders in one parliament would be more than the country could tolerate. This side of the general election, the die is cast. After the election is another matter. So far, so fairly obvious. But here’s a thought. If Rishi Sunak leads the Tories to defeat this autumn, as most of his MPs now suspect will happen, he should not then resign immediately. Instead, Sunak should stay on as opposition leader. British politics doesn’t need a premature pre-election leadership contest of the sort that was again floated this week. But it doesn’t need a premature post-election contest either. And nor, in particular, does the Conservative party. Think it through. The UK general election takes place on, let’s say, Thursday 17 October. The Conservatives suffer the defeat that the opinion polls are currently suggesting. Keir Starmer becomes prime minister, with a working, and maybe a very large, overall Labour majority. A four- or five-year Labour term looks likely. Sunak himself holds on in his Richmond and Northallerton seat. The result – his is a huge rural constituency – is not declared until around 4am on Friday 18 October. He flies back to London, arriving in No 10 as the sun comes up. He has already phoned Starmer to concede. Now he phones defeated colleagues to commiserate and thanks aides for their support. Then, around breakfast, he steps out into Downing Street and makes a statement. What does he say? Recent precedent suggests he says something graceful about the honour of serving and then resigns the party leadership. That’s what Gordon Brown, the last incumbent prime minister to lose an election, eventually did in 2010. It’s what John Major, the last losing incumbent before Brown, did in 1997 too. If he takes this course, Sunak would remain as leader while a successor was chosen. Then, around Christmas, he would disappear into the rest of his life, perhaps resigning as an MP and triggering an early byelection in North Yorkshire. But Sunak does not have to do this. He is under no compulsion to quit. Defeated prime ministerial incumbents of the postwar period, such as Clement Attlee in 1951, Alec Douglas-Home in 1964, Harold Wilson in 1970, Edward Heath in 1974 and James Callaghan in 1979 all stayed on as opposition leaders for a period. Wilson even returned to the prime ministership in 1974. Defeated opposition challengers, from Winston Churchill in 1950 through to Jeremy Corbyn in 2017, have also stayed on. Yet there remains a creeping default assumption in our political culture, fed by an impatient media, that a defeated party leader ought to go immediately. Neil Kinnock did this as opposition leader in 1992. So did William Hague in 2001 and Ed Miliband in 2015. David Cameron resigned as soon as he lost the Brexit referendum. Alex Salmond did the same after the Scottish referendum. Many Tory MPs seem to take it as read that Sunak, if he loses office, will do the same thing. He should not do so. Instead Sunak should stay on as Conservative leader if he loses the election. He should prepare the ground for staying on with trusted colleagues. He should then stand at the Downing Street lectern and say responsible leaders do not just jump ship. He should say it is his duty to see the party through a period of necessary reflection. He could even say what Callaghan told Labour MPs in 1979: “There is no vacancy for my job.” But he needs to have a plan for what he can bring to opposition as well as a plan to then leave later. Here, Michael Howard could be the model. Howard stayed five months after losing the 2005 election before resigning. This had important consequences. The leadership election process was rethought, though not as radically as Howard wanted, and the shadow cabinet was reshaped. This allowed younger faces to catch the spotlight. The result was the election of David Cameron. Sunak should think in similar terms. There are powerful civic reasons for him to stay. Politics and government need some restoration of continuity and stability. There should never again be three prime ministers or four chancellors in a single year. Ministerial careers should not average a mere eight months, as they have since 2019. Parts of the Tory party are spoiling for yet another fight, as is the Tory press. They need to be hosed down, not fired up. Politics needs to be about the good government of the nation again. There are partisan Conservative reasons why Sunak should stay, too. The post-Brexit Tory party needs to work out what it now stands for, and to rebuild, if it can, in a united way. Its current divisions are unsustainable. The post-election numbers – and the bits of Britain they speak for – will make a lot of difference. The mood, priorities and sense of political discipline will feel very different with, say, 280 surviving Tory MPs than if there are only 180, or even a smaller number still. For Sunak to quit while the general election dust has not settled is simply the worst way of addressing these challenges. To do so would maximise the potential for making bad choices. This was how Labour inflicted Corbyn on itself after Miliband’s narcissistically premature resignation. The Tories could very easily do something equally harmful to themselves if Sunak walks away too soon after a Tory defeat. That is why he should stay on until the summer of 2025. Only then should he depart as party leader. Martin Kettle is a Guardian columnist