When Labour went down to defeat last May, Hilary Benn came close to quitting the shadow cabinet. “He almost did a Harriet,” says one of his friends in reference to Harriet Harman’s decision to retire from the front rank. Having turned 60, he thought his race was almost run. Even if he had the ambition, he had no prospect of ever leading the Labour party. Other MPs had always spoken of him as one of the nicest men in parliament, but they also struggled to pick out anything notable from his career, even though it had encompassed seven years in the cabinet. I recall one of his colleagues saying to me: “I like Hilary as much as the next person, but what is the point of him?” Where his father, Tony, had been a mesmerising rhetorician and a massively polarising figure, the cautious Hilary seemed the exact opposite: neither offensive nor inspirational to anyone. Among the wider public, in so much as he was known at all, it was for being the son of a much more famous Benn.

That changed in the 15 minutes that it took him to deliver his electrifying speech at the climax of the marathon debate on Syria. It was a bravura performance for both reminding the left of its proud history of fighting fascism and for confronting the absurd claim of some opponents of action against Isis that all the moral arguments are their exclusive property. For added piquancy, it was delivered in front of and in defiance of that disciple of the elder Benn, a scowling Jeremy Corbyn. After delivering a piece of oratory as powerful as anything ever produced by his father, Hilary Benn is now a polarising figure himself. Only the polarities are inverted. The sort of people who worshipped the elder Benn have been enraged by the son. “Hilary Benn, shame on you!” chanted some of the protesters in Parliament Square. The sort of people who were frightened by his father express admiration for the son.

Does this make him, as the bookies and some of his colleagues now have it, a Labour leader in waiting? That I rather doubt. Having defined himself so explicitly against Mr Corbyn on such a litmus issue within the party, I can’t see Mr Benn winning a leadership contest unless there is a dramatic shift in the opinions or the composition of Labour’s membership. He insists that he has no interest in being leader anyway. “The game plan is there is no game plan,” says one of his confidants. Many other politicians would have milked the moment by answering the clamorous interview requests from the media that came in after the speech. Yet since his tour de force on Wednesday night, Mr Benn has been notably absent from the airwaves.

That has not prevented a sudden explosion in Hilary Benn studies, a hitherto neglected area of research at Westminster. What is he up to? What does he want? How does he plan to get it? This is being most intensely asked by those around Jeremy Corbyn where Mr Benn was already identified as an enemy for heading resistance to the leader over Europe and the nuclear deterrent. “They are completely paranoid,” remarks one member of the shadow cabinet. I guess his team would reply that Mr Corbyn has plenty to be paranoid about.

Labour’s internal tensions have been slightly eased by the result of the Oldham West and Royton byelection. Had the seat been lost, or won only by the narrow margin expected by many Labour people who campaigned there, it would have triggered another burst of speculation about a coup attempt against the leader.

But note that Labour cannot even enjoy a victory these days without quarrelling about it. Barely had the returning officer spoken than the two sides were doing battle over how to interpret the result. Mr Corbyn rushed north in an attempt to claim Labour’s reduced majority in the seat as a seal of approval for his leadership. His internal opponents contend that Labour’s better than expected performance was achieved not because of, but in spite, of the leader. They point out that the new MP, Jim McMahon, is no Corbynista, ran on his record as the leader of the local council and was reluctant to have Mr Corbyn’s face on any of his campaign literature. The most sensible assessment of Oldham is to say that it tells us nothing terribly useful about Labour’s capacity to win more important elections under its current management. The Labour vote share went up in Oldham by almost precisely the same amount as it did at byelections during Ed Miliband’s first year as Labour leader – and we know how that story ended.

The immediate question now facing Labour is whether the furies unleashed by the divisions over Syria will abate. That will depend on how Mr Corbyn behaves. Does he sincerely want to put a stop to the intimidation of Labour MPs or does he secretly regard the menacing levels of abuse being directed at them as a useful weapon in his struggle to impose himself on dissident parliamentarians? Labour MPs who supported the extension of action against Isis – and even those just weighing up the arguments for and against – have become the targets of a bombardment of hostile demos, tweets, emails and phone calls. When it comes to the rough and tumble of politics, I’m usually of the Harry Truman view: if you can’t take the heat, get out of the kitchen. But the poison being unleashed by some hard left activists, which includes death threats, takes us into extremely dark territory. Funny, isn’t it, how some of those who claim to be dedicated to peace so relish threatening violent retribution on anyone who has the temerity to disagree with their world view?

There is a fairly obvious strategy at work here. Frightening and demoralising Labour MPs is designed to quell criticism of Mr Corbyn among his parliamentary colleagues. Some Labour MPs accuse him of giving the abuse his tacit encouragement when he remarked that MPs who backed military action would have “no hiding place”. Left Unity, a hard left group that cheers for him, has issued a “traitor list” of the 66 Labour MPs who voted in favour of extending air strikes against Isis. It yells: “Labour warmongers… deselect them now.” Using milder language, but speaking with the authority of someone appointed to an official position by Mr Corbyn, Ken Livingstone has endorsed the idea of a purge.

I don’t think that will happen in the short term. The cannier operators in Camp Corbyn can see that an early escalation to deselections would backfire. They could not prevent a deselected Labour MP from continuing to sit in the Commons as an independent. Or the victims of a purge might resign to trigger byelections at which they could run as True Labour or Real Labour. So purely as a matter of tactics, it makes no sense for the Corbynistas to go after Labour MPs at this stage. They will bide their time until closer to the next general election. They do not need to introduce compulsory deselection for there is already a procedure for triggering it. Furthermore, when the Tories move to redraw the constituency boundaries, there will have to be selection processes for the new seats anyway. That will be the hard left’s big opportunity to try to take out Labour MPs on the grounds of disloyalty and ideological deviancy.

This goes to a fundamental question about the role and obligations of an MP. To whom ultimately should a parliamentarian be accountable? Are they there to serve the leader? Are they there as delegates for their party members? Is their role to obey the demands of their constituents? Or do they follow Edmund Burke’s classic formulation that the highest duty of an MP is to exercise his or her individual conscience and judgment? “It ought to be the happiness and glory of a representative to live in the strictest union, the closest correspondence, and the most unreserved communication with his constituents. Their wishes ought to have great weight with him; their opinion, high respect; their business, unremitted attention… But his unbiased opinion, his mature judgment, his enlightened conscience, he ought not to sacrifice to you, to any man, or to any set of men living… Your representative owes you, not his industry only, but his judgment; and he betrays, instead of serving you, if he sacrifices it to your opinion.”

I lean to the Burkeian definition of the role of an MP. I’d rather have his or her honest judgment than a slavish obedience to opinions imposed on them. But there is no law about this. Most MPs manage to muddle through, answering the accountability conundrum by striking compromises between their own opinions and the sometimes conflicting demands of their leadership, their members and their constituents. The trouble in today’s Labour party is that there isn’t much of an option for MPs to muddle through. The divisions are too stark, the fear and loathing is too ferocious.

One of the more unpleasant and untrue things said about Hilary Benn’s speech was that it would have disgusted his father. Benn the elder would have been on the other side of this debate, but a notable feature of their relationship was that they always kept their disagreements friendly. That is an art that the Labour party has entirely lost under Jeremy Corbyn.