This may be Rishi Sunak’s best chance to seize the crown. But will he dare to take it?

Anyone who stays in the cabinet is complicit with Boris Johnson. The chancellor’s window for action is shrinking fast

He sits there silently on the frontbench, the man with nothing to say about the great swirl of chaos all around him. What is Rishi Sunak thinking? “There is a tide in the affairs of men. Which, taken at the flood, leads on to fortune.” Miss it, warns Brutus the conspirator, and all his life will be “bound in shallows and in miseries”. Indeed, this chancellor may never get another chance to shoot through to No 10.

But when exactly is that damned tide at the flood? When Gray’s anatomy of No 10 parties is published, perhaps. Or when those notoriously dilatory plods report? Boris Johnson hopes that delaying the partygate reckoning will allow him to fortify his dam against that flood. His backers try to frighten Tory MPs by threatening that a new leader means a general election.

Sunak sees Ladbrokes’ latest betting odds showing his chances of succession at 11/8, while the foreign secretary, Liz Truss, trails at 6/1. The old Tory superstition says the hand that wields the dagger never wears the crown, but this is a time of broken Tory traditions. Sunak rides high as a small-state, low-tax, fiscal austerian – always a true Brexiter. But when to strike? Former political adviser Dominic Cummings has been his promoter, engineering the resignation of Sajid Javid from the Treasury to make way for Sunak as his protege. But that’s not a great calling card right now.

Doubts about him in his party focus on his slender political experience – such a thin record fails to reveal if he has the stuff of leadership in him. His meteoric rise has left little trail behind him. All that we know is that he has glided effortlessly upwards, from Winchester to PPE at Oxford to a Fulbright scholarship at Stanford; then onwards to Goldman Sachs and hedge fund management, making his fortune. He danced into one of the very safest Tory seats, with a majority of 23,000. Along the way he married into a billionaire family. Last year he was challenged on a possible failure to declare his wife’s shareholding in Infosys, which has held contracts with government ministries and public bodies; the sums involved were so vast that she was revealed to be richer than the Queen. Burnishing his memories of a summer vacation once working as a waiter in the restaurant of a family friend looks as absurd as most attempts to deny privilege. Why should a high-flying Tory need to?

The doubts are about his untested character, his fortitude, daring, imagination, political nous and agility; whether he can balance an instinctive feel for his party’s and the public’s mood while still steering the ship of state in a purposeful political direction – the ingredients of good leadership. Some or almost all of those have been missing from recent Tory leaders, and he would be their fourth in just six years. Tory MPs and members have not been good choosers.

He sits there, as invisible as possible, waiting for the premiership to drop, ripe and ready, into his lap – like everything else in his life. But waiting for his party to bring it to him on a silver platter is not the look of a leader, especially while so many of his colleagues are humiliating themselves defending Johnson’s indefensible behaviour and preposterous lies. Sunak neither defends nor attacks, but to use Johnson’s metaphor, waits at the back of the scrum for the ball to come loose.

One of the valiant is Truss, out there proclaiming, mendaciously, her “hundred per cent support of the prime minister”, dutifully listing his Brexit and vaccine rollout triumphs. Hers is the better part of valour, not his silent discretion. Anyone who stays in the cabinet, or indeed any Tory MP waiting without declaring, is complicit in everything that has been revealed so far about the nature of Johnson and his regime. As long as ministers draw their salaries they should back their leader, at least in public. (Truss’s “fizz with Liz” private wooing of MPs for when that ball finally emerges is another matter.)

If Sunak resigned, Johnson would be done for, as Theresa May was when Johnson resigned as foreign secretary. If the chancellor wants to prove his leadership qualities, he should refuse to be party to all this dishonesty, be brave, and make his pitch as a clean pair of hands. Otherwise that silver platter may pass to someone willing to fight for it.

If Johnson clings on, possibly surviving a confidence vote, he will bow to blackmail from the rightwing MPs now filing in to see him, demanding he “be a real Conservative”. He already flails around for totemic rightist acts as they urge more culture wars, more curbing unemployment benefits, assaulting the BBC, pushing back migrant boats, getting rid of “green crap” policies for net zero targets, cutting spending and not raising national insurance – even as the NHS and schools flounder. These true believers ignore Johnson’s clever “levelling up” electoral trick, which attracted voters with false promises of a spending bonanza.

If Sunak vacillates now, the brutal results of all the above will soon bequeath him an angry electorate drowning in bills, with inflation rising above their falling pay. The halcyon days of “eat out to help out” will be long obliterated by his austerity years. If he does seize the crown, calling a general election now might be his best chance. Labour hopes a lame Johnson limps on.

• Polly Toynbee is a Guardian columnist