‘Tell me but this. What rebel captain,/ As mutinies are incident, by his name/ Can still the rout?” asks Sir Thomas More in the eponymous Elizabethan play, part-written by Shakespeare. “Who will obey a traitor?”

Who indeed? As we have grown ever more habituated to the likelihood of Jeremy Corbyn’s coronation as Labour leader on 12 September, so the quest has intensified for parallels and precedents. Naturally, those looking for navigation mine the history of the left, or look for contemporary symmetries in the examples of Syriza and Podemos.

A less obvious resource is the recent history of the Conservative party and, specifically, the brief, unhappy leadership of Iain Duncan Smith, the Maastricht rebel turned party boss. Before a hundred tweet-grenades are unpinned – easy, there – let me be quite clear that I grasp fully the differences between the two politicians.

For a start, Corbyn would never describe himself as “the Quiet Man”: when necessary, his speakers go up to 11. IDS cannot claim to have galvanised the young, or inspired many thousands of people to register their support for his party. Between 2001 and 2003, it was his bleak fate to pass through the public’s consciousness without grazing the sides.

But the parallels between the bearded one and the bald one are real. Like Duncan Smith before him, Corbyn is a mutineer set to be catapulted to the role of chieftain. Like Duncan Smith, he represents an ideological base: not Euroscepticism and neo-Thatcherism but post-crash, anti-austerity socialism.

In selecting IDS, rather than Michael Portillo or Kenneth Clarke, the Tory party chose to please itself rather than to face electoral reality. The same will be said of Labour if it chooses Corbyn as the person to remedy the failures of the last election (though Corbyn’s supporters assert that what is and what is not “electable” is changing fast).

Like IDS before him, I think Corbyn – assuming he wins – will launch himself as a unifier and a healer, calling for unity and deploying what he is already calling an inclusive tone. Duncan Smith, it is now almost universally forgotten, surprised his own followers by embracing the “necessary and sometimes painful process of modernisation”. He directed his party’s focus away from Europe and towards the public services and social justice.

Whatever has been going on behind the scenes, Corbyn’s tone throughout this contest has been irenic, collaborative, generous. If he wins, just watch him play the part of team coach rather than that of purging commissar. He has quoted Lincoln’s second inaugural address of 1865: “With malice toward none, with charity for all”.

As Tory leader, Iain Duncan Smith passed through the public’s consciousness without grazing the sides

Yet the structural problem that Corbyn still faces is precisely what did for Duncan Smith. In 2001 Douglas Hurd, a former foreign secretary and one of the architects of the Maastricht treaty, was uncharacteristically blunt about what IDS could expect as leader. “There will be continued divisions because people will follow their convictions, as he did. Iain Duncan Smith made his reputation by following his own convictions, certainly, but by undermining, in concert with the Labour party, what we were trying to do in Europe. He can’t really call on any automatic loyalty, against that background.” So it proved. Portillo, Clarke and other prominent Tories declined to serve on IDS’s frontbench.

The leadership election rules devised during William Hague’s tenure of office had given Tory MPs the task of whittling the field down to a two-person shortlist, which was then put to the entire membership. Clarke topped the final ballot of MPs with 59 supporters, ahead of IDS on 54 (and Portillo, who was knocked out, on 53). But in the deciding ballot, of members, Duncan Smith easily defeated Clarke – who had been chancellor, home secretary, health secretary and education secretary – by 61% to 39%.

The problem for IDS was that the formal power to sack the leader remained with Tory MPs. As Timothy Heppell writes in a forthcoming volume, British Conservative Leaders, edited by Charles Clarke, Tim Bale and others: “A leader who was previously a backbench rebel looks like a hypocrite when as leader they demand loyalty is owed to them.” The contradiction erupted in November 2002 when IDS, backtracking on his professed interest in party modernisation, foolishly imposed a three-line whip on Tory MPs to vote against gay adoption.

In response, eight voted with the Labour government and 35 abstained. To compound the folly, he held a press conference inviting his colleagues to “unite or die”. He lasted another year as leader, but the die was cast. Most extraordinarily, the whips’ office abandoned its normal function and sought not loyalty but clarification. That came, brutally, in the vote to unseat Duncan Smith on 23 October 2003, which he lost by 90 votes to 75.

What does all this Tory lore have to do with brave new Jeremy? In the current New Statesman Mike Gapes MP is quoted thus: “I’ll show him [Corbyn] as much loyalty as he showed other leaders.” Which is to say: not much. Yvette Cooper, Liz Kendall, Chuka Umunna and others have already said or signalled that they would not serve on his frontbench. Between 1997 and 2010, Corbyn defied the whip 238 times. That’s a lot of “conscience”. It’s also a very weak position from which to demand loyalty.

Corbyn’s team will say his mandate is different to, say, Ed Miliband’s: it is a people’s mandate, an acclamation that marks the rebirth of the Labour party as a mass movement. But for all its populism and quasi-presidentialism, the British system remains parliamentary in practice as well as theory. Modern leadership contests are so constructed that a politician can win by behaving like a US presidential candidate in a primary. But staying leader is a different matter. A party leader who loses the confidence of his MPs is in big trouble.

Given his history, the parliamentary Labour party will support Corbyn only in so far as he looks like a winner. Don’t forget: this lot got rid of Tony Blair, a three-time destroyer of the Tories, as soon as they judged him a liability. Do you think they will hesitate for a second if they think their seats are at risk? Beware the ides of March, Jeremy – and every other day, for that matter. As Duncan Smith could tell him, winning the leadership is the easy part.