The prime minister has cemented his reputation as a careless pair of hands and the leader of the opposition has struggled to make his voice heard. There is only one senior British politician to have got through the past 18 months with consistently positive approval ratings from both the voters and his party’s members. Take a bow, Rishi Sunak. The humiliating exit from Afghanistan is further enhancing his standing among Conservative MPs, if only because it has diminished the stature of rivals. The Tory backbenchers who queued up to lambast the prime minister in the Commons see further evidence that Boris Johnson is no good in a crisis. Reputational damage has also been inflicted on the prime minister’s titular deputy, the foreign secretary, Dominic Raab. If a contest to be the next leader of the Conservative party were to be held tomorrow, the chancellor would be the man to beat. Which is a highly exposed position to be in. When an heir-apparent is all too apparent, he attracts a coterie hoping to prosper by clinging to his coattails. He also foments envy among piqued colleagues and breeds suspicion and distrust at Number 10. No prime minister likes to hear one of the cabinet being described as a successor. It reminds them that they are mortal. Tony Blair and his staff expended gigawatts of nervous energy trying to work out whether Gordon Brown, a powerful chancellor ravenous to move next door, was on manoeuvres. As he very often was. In the late 1960s, Harold Wilson’s paranoia levels spiked whenever Roy Jenkins received positive reviews for his helmsmanship of the Treasury. The relationship between Margaret Thatcher and Nigel Lawson, erstwhile ideological soulmates, deteriorated into such bitterness that he eventually resigned, his exit from the Treasury beginning the chain of events that led to her downfall a year later. As in that case, it is sometimes fissures over policy that drive apart the Downing Street neighbours. On other occasions, the struggle boils down to who wields the power, which was at the root of most of the Blair/Brown psychodramas. Policy, power and personality are all playing a role in the rising tensions between the current pairing in Downing Street. One reason for Mr Johnson to resent Mr Sunak is that he is not the chancellor that the prime minister thought he was getting when he promoted the much younger man to Number 11. His expectation then was that he would be an unshowy and pliant next-door neighbour willing to rubber-stamp all the cheques that the prime minister wanted to cash to make himself popular. Mr Johnson would be the great showman and a modest chancellor would stay behind the scenes, dutifully hunched over the Treasury’s spreadsheets trying to make the numbers add up. The actual Mr Sunak is keen on self-promotion with a talent for charming Tory MPs. He is much more liked than the prime minister and no one believes him when he protests that he has no ambition to reach the very apex of the greasy pole. He has grown more confident in throwing the Treasury’s substantial weight around in battles with an often dysfunctional Number 10. Internal policy disputes have repeatedly surfaced in the media over recent months, always a sign of rising stress and fraying collective discipline in Downing Street. The arguments have ranged from who should pay for reform of social care to how to fund the greening of homes and what to do about the pension triple lock. In more than one case, the chancellor’s view seems to have prevailed over that of the prime minister. When a relationship goes sour, it is often the trivial spats that reveal the most. Earlier this month, the Sunday Times reported that the prime minister had received a letter from the chancellor in which the latter argued for a substantial easing of Covid-related travel restrictions to help the economy, a position very popular among the Conservative MPs who Mr Sunak spends a lot of time wooing. The prime minister was reported to be “apopleptic” about this relatively minor leak. Not because he was opposed to loosening the travel rules, but because the leak appeared designed to make it look as if a dithery prime minister needed a push from the decisive next-door neighbour. The prime minister told a meeting with aides that he was toying with demoting Mr Sunak: “Maybe it’s time we look at Rishi as the next secretary of state for health.” Some dismissed this as no more than a Johnsonian jest or passing temper tantrum. A different thought occurred to me when I learned that the remark about evicting Mr Sunak from Number 11 was witnessed by more than a dozen people. Mr Johnson is a journalist who made this provocative suggestion to a large audience made up of people who talk to journalists. I reckon he expected it to reach the public domain and was happy for it to do so as a way of sharply reminding his neighbour who was the boss. Allies of the chancellor then retorted that, rather than accept a demotion, he would quit the cabinet and sit on the backbenches waiting for Mr Johnson to fall. Another aggravation for the prime minister is the way in which he has been relentlessly pummelled for his handling of the pandemic, while the chancellor has been largely unscathed by criticism even when he was responsible for egregious blunders. His “eat out to help out” scheme last summer was caustically referred to as “eat out to help out the virus” by some government scientific advisers, but all the blame for the disease’s resurgence landed on Mr Johnson. He was certainly extremely culpable. According to the retelling of Dominic Cummings, the prime minister was so resistant to further lockdowns that he was prepared to “let the bodies pile high”. Yet there have been points in the pandemic when the chancellor was pressing so aggressively for Covid restrictions to come off that he wanted to take risks with the virus that alarmed even Mr Johnson. So much so that I am told that the prime minister was heard to refer to the Treasury as “the pro-death squad”. Jealousy may be another factor at work. Mr Johnson’s personal money troubles are a persistent topic of conversation among his friends and a source of stories that generate a stink. Mr Sunak, a former investment banker married to the daughter of a billionaire, pointedly let it be known that no Tory donors were involved when his Downing Street flat was refurbished. The Treasury declared that the bill was paid from his own deep pockets. The richest MP in the Commons, he has just received planning permission to put in a swimming pool, gym and tennis court at the Grade II-listed manor house where he lives when in his north Yorkshire constituency. That will do as a facsimile of Chequers until he gets a chance to bid for the real thing. A further source of grievance for the prime minister, and among some cabinet ministers, is that the chancellor was deft at pocketing the popularity he gained from his Covid emergency measures, but artfully swerves the opprobrium when people are left disappointed by his decisions. After the Treasury refused to cough up for a schools catch-up programme devised by the prime minister’s adviser, who promptly resigned in protest, most of the fire was directed at Number 10 and the hapless education secretary. It is against this background of paranoia and recrimination in Downing Street that the government is heading into an autumn during which spending and debt will be dominant and highly divisive issues. The bill for the pandemic, which is already coming in north of £400bn, has added massively to government borrowing. At the same time, there is a host of demands for more spending to tackle the long Covid legacy. The NHS has a huge hangover of postponed treatments to deal with and a large number of cases are backed up in the courts, to take just two of many examples. The autumn spending review will amplify the split between the fiscal disciplinarians in the Tory party and those who think there is no vice in being a big borrower in the aftermath of a crisis. That is the great faultline between a chancellor who is a fiscal conservative at heart and a cakeist prime minister who is ever desperate to please the crowd. Prime ministers and chancellors can navigate differences of temperament if they are philosophically aligned. They can resolve policy disputes when they trust each other. A relationship made toxic by personal resentments, ideological differences and rival ambitions is a highly combustible cocktail.