Much in demand as an after-dinner speaker, Michael Gove used to quip that his gravestone would bear the epitaph: “They couldn’t get Boris.” In their college days, the lord chancellor and the former mayor were both presidents of the Oxford Union – the university debating society that fancies itself a training ground for the House of Commons.

Yet their paths diverged dramatically under David Cameron’s leadership. In Dave’s gang, Gove has been the wordsmith, radical reformer of public services and foreign policy neocon, especially close to George Osborne. Though fond of the “Gover”, Boris was never part of the gang, preferring to nurture his own stardom under a single spotlight.

How, then, did they end up as a double act, ranged against Cameron as a government within a government? Last week Vote Leave’s two leading lights attacked the prime minister’s failure to achieve his own immigration targets. On Sunday, they took Cameron and Osborne to task over the economic implications of EU membership, alleging the government’s failure to stand up to Brussels has been “damaging to public trust”.

The five-page letter continues: “The public cannot trust EU or government promises that we won’t be paying for eurozone bailouts given the history and how we can be outvoted.” The core of the charge is that continued EU membership exposes British citizens “to pay unexpected bills” – in spite of the European commission’s failure to produce “evidence of significant gains from the single market”.

Notionally a routine tactic in the referendum campaign, this is in practice the riskiest attack yet by the Gove-Johnson axis. Little more than a year ago, the Tory party triumphed with an election strategy that remorselessly emphasised its stewardship of the economy as the heart of its claim to a second term. Now two very senior Conservatives are publicly questioning the integrity of that stewardship. As one Cameron ally puts it: “They are like a couple of tutorial partners sniggering at their tutor.”

The elegance of the letters’ prose is a distraction from their surgical brutality. It is one thing to make respectful use of the very specific suspension of collective cabinet responsibility (though not a senior minister, Johnson is a member of the political cabinet). It is quite another to launch a systematic series of attacks on the prime minister and his chancellor – attacks that will undermine them whatever the result of the 23 June vote.

The cold fury of John Major on Sunday’s Andrew Marr Show was the exasperation of a former PM who knows how this particular movie ends. The Vote Leave campaign, he said, was “verging on the squalid”. The NHS would be as safe with Johnson, Gove and Iain Duncan Smith as “a pet hamster would be with a hungry python”.

In 1995, Major tried to unite his fractious party with the shock and awe of a leadership contest, resigning and encouraging rebels to “put up or shut up”. In the ensuing contest he defeated John Redwood – but to no avail. The virus of disunity could not be contained, and contributed significantly to the party’s electoral destruction in 1997.

A united party is not one where the leader yields to every demand and forgives every offence

Despite the warnings by Major and other veterans of past Tory wars, I am not sure the party at any level grasps how deadly its predicament truly is. It looks across the dispatch box at Jeremy Corbyn’s team and is filled with the warm glow of complacency. But this is a huge mistake. Complacency at moments of crisis is the mother of unthinkable outcomes.

If Cameron prevails on 23 June, he will have a windfall of political capital and would be well-advised to spend it with ferocious speed. As Ben Pimlott, Harold Wilson’s biographer, observed, victory in the 1975 referendum enabled the prime minister to pursue “the chastisement of Tony Benn, and the emasculation of the Labour party’s industry policy, which Wilson had long opposed and with which Benn was closely identified”.

Joe Haines, Wilson’s press secretary, sought from Benn an “unqualified assurance that you accept the principle of collective responsibility and that you will from now on comply with its requirements and the rules that flow from it”. Wilson moved Benn from industry to energy and Judith Hart, another anti-EEC leftwinger, resigned to avoid demotion. Predictably furious, Benn told Wilson: “It is a basic trade union principle that you do not victimise people after a strike.”

If Cameron wins, he will be urged by some to show similar clemency, on the grounds that the nation has had a lively debate, reached a conclusion, and must now come together singing Kumbaya.

In the Mail on Sunday, the PM let slip the anger he is clearly feeling. The leave campaign’s argument “is let’s wreck the economy by leaving the single market in order to do it. I’m going to make them pay for that.”

Yet in the same interview he also appeared to promise an unconditional amnesty to the senior Brexiteers. Asked if they would be sacked, Cameron replied: “No. We have to bring the party back together. I’ve always believed in having the big players on the pitch.”

No doubt. But the mark of a great manager is to know when a player – however skilled, however popular – needs to be benched, or even sacked.

It is one thing to be a conciliator; quite another to be a pushover. No structure of authority can long survive if there are not clear consequences for transgressions.

Let’s be frank: does Cameron really believe the Brexiteers will be as merciful to him if he loses? The hardcore of backbenchers who loathe him are longing for a confidence vote and a merciless battle to replace him with Johnson as soon as possible. This plan is all but public – demeaningly so for Cameron.

A united party is not one where the leader yields to every demand and forgives every offence. A united party is one where the leader combines breadth of support with a recognition of behavioural limits and the authority to enforce them.

One may smile, and smile, and be a villain. Not all the friends Cameron started with in 2005 are his friends now.

During this campaign, some of his most senior colleagues have formed what amounts to a pop-up counter-government. If he gives them a free pass, he will be condemning his own party to a bedlam that will long outlast his leadership.