Always read the small print. Buried in the detail of George Osborne’s ersatz budget was a nasty little ruse to hurt the Labour party. It is to be deprived of £2m in “short money”, the support given to help the official opposition perform its vital function of holding the government to account.

This slanting of the playing field will also cost the smaller parties, is certainly mean and arguably anti-democratic. It is also hypocritical coming from a chancellor who seems to employ at least 10 special advisers at the taxpayers’ expense. My compliments to John Rentoul, my rival at the Independent on Sunday, for drawing our attention to the chancellor’s swollen entourage. It is also absolutely unnecessary. The Conservatives don’t need to stoop to such partisan spite. Not when the Labour party is making such a first-class job of eviscerating itself.

In the short history of the Corbyn experiment, the past seven days have been the most spectacularly disastrous yet. There’s open civil war between the leader and his shadow cabinet over Syria. There’s Ken Livingstone telling the Question Time audience that the 7/7 bombers “gave their lives” as a protest against the invasion of Iraq, as if the killers of 52 people were in some way martyrs to a noble cause. We have Labour MPs calling for Mr Corbyn to resign while the leader’s office mobilises constituency activists to try to intimidate the parliamentary party. As if all that was not quite enough immolation for one week, we were also treated to John McDonnell’s calamitous response to George Osborne. It ought to have been a humiliation for the chancellor when he abandoned his cuts to tax credits. This was not any old U-turn. This was a tyre-shrieking, tarmac-smoking, whiplashing U-turn, a complete reversal of a central plank of the July budget that he produced just four months earlier.

A half-competent shadow chancellor would have lacerated him for that and at the same time pointed out that the Tories are only postponing a squeeze on the incomes of the working poor. There was plenty more for Labour to seize on in a financial statement that should have left Mr McDonnell spoilt for choice of ammunition. He might have ridiculed this supposedly prudent chancellor for gambling everything on a long-term weather forecast of uninterrupted sunshine from the Office for Budget Responsibility that is almost certain to be wrong. He could have spotlighted the hike in council tax to pay for the gaping holes in social care left by spending cuts or he might have mocked the chancellor for busting his own welfare cap. John McDonnell did none of that in a performance that made me feel a surge of nostalgia for Ed Balls. Now, of course, it was intended as a joke when the shadow chancellor dug into his pocket, extracted a well-thumbed copy of Chairman Mao’s Little Red Book and then, to stunned looks on the faces of Labour MPs and joyful smiles from Tories, started to read from the collected thoughts of a dictator who murdered many millions of his own people.

There was a second difficulty with trying to be funny about Mao that was particular to this shadow chancellor. When one of the charges against you, not least by your own colleagues in parliament, is that you represent the capture of the Labour party by the far left, it is probably best to avoid flourishing a communist text from the despatch box. Little wonder George Osborne looked like all his Christmases had come at once. What should have been a red-faced day for him became a red-letter day thanks to the shadow chancellor’s self-harming stunt.

This illustrates that the problem with the people currently at the top of the Labour party is not simply to do with their ideological complexion or their back catalogue of incendiary quotes. It is that they are simply bad at politics. And by being rubbish at politics, the people they most let down are those many millions of Britons who need a credible Labour party providing an effective opposition.

I guess Labour MPs ought to count it a blessing that Jeremy Corbyn did not respond to David Cameron’s statement about Syria by quoting from Lenin’s What Is To Be Done?. His performance over this issue exposes another problem with his brand of politics. Given the experience of previous military action in the Middle East, the Labour leader ought to have an excellent chance of persuading people when he asks whether it is sensible to extend air strikes against Isis to targets in Syria. Yet he is the worst advocate for the positions that he holds. He is so unconvincing that he cannot even persuade his own shadow cabinet. He is at odds with the shadow foreign secretary, the shadow defence secretary and his deputy leader, all of whom are more persuaded by the prime minister than they are by their own leader. When they met to discuss their position on Thursday afternoon, just five of the 31 members of the shadow cabinet supported the leader. Why? I think it boils down to this. There would be a more attentive audience for the Labour leader’s case if anyone thought he was opposed to air strikes because he has weighed up the many political and moral complexities of the Syrian situation and come to a reasoned conclusion that the course of action proposed by the prime minister is unwise.

But his arguments, even the good ones, come over as weak because everyone suspects that there are no circumstances in which he would ever want Britain to act to protect its citizens and assist its allies. He has previously said as much. During the leadership contest, he was asked if there were any circumstances in which he would deploy military forces and replied: “I’m sure there are some but I can’t think of them at the moment.”

Pacifism is a principled position. It is just not one that is shared by the great majority of the British people or the great majority of folk who voted Labour at the last election or by the great majority of Labour MPs. When YouGov recently asked voters to say who they trusted to make the right decisions about Isis and Syria, no one came out especially well. David Cameron is narrowly more trusted than distrusted. Two people came out very badly: 68% of people do not trust Jeremy Corbyn to make the right decisions about Syria and Isis, precisely the same percentage as those who distrust Vladimir Putin. On this critical issue of national security, voters have no more faith in the Labour leader to act in the best interests of Britain than they do the president of Russia. Had someone polled the shadow cabinet, the Labour leader would have come out even worse with his senior team than he does with the British public.

There was never much trust between him and his colleagues and now it has collapsed. Hilary Benn wasn’t given sight of Mr Corbyn’s Commons speech about Syria even though he is shadow foreign secretary. The leader did not tell his shadow cabinet he was going to announce his position in a letter to MPs and then conduct a snap referendum of Labour members via email. It is hard to know whether these were deliberate acts of bad faith – the charge from some infuriated members of the shadow cabinet – or just blithering incompetence.

Since the differences are so irreconcilable between the leader and his senior team, most expect that Mr Corbyn will have to concede to a free vote of Labour MPs when the shadow cabinet meets again on Monday. That sets the stage for the leader of the Labour party to be in one voting lobby while up to half of his MPs, including a big majority of the senior frontbench, will be in the other on this grave and momentous issue.

“We can’t go on like this.” That’s the cry now to be heard from all points of the Labour spectrum, left, right and centre. You hear it even from Paul Flynn, the veteran Welsh MP who hails from Mr Corbyn’s wing of the party, who says that the current situation is “impossible”. Even more Labour people will be saying “we can’t go on like this” if this week’s Oldham West and Royton byelection sees a collapse in the Labour vote. The howls of despair will be louder still if Labour loses the seat to Ukip.

Yet it seems most probable that Labour will go on exactly like this. For there is no obvious escape route from the party’s agonies. Some voices urge the shadow cabinet to threaten Mr Corbyn with mass resignation to force him to step down. Trouble is he can simply refuse to quit so the only effect of a mass resignation would be to render Labour even less functional as an opposition. A coup by Labour MPs is much talked about, but that will be counter-productive for so long as it looks likely that the members would just re-elect him. And that does look highly likely. His opposition to military action, a touchstone issue for a lot of Labour’s current membership, will serve to make him more popular with many of them.

Labour is trapped. Trapped with a leader incapable of commanding the confidence and loyalty of his MPs. Trapped because Labour’s aghast parliamentarians are powerless to do anything about it. Trapped with a leader who can’t win the trust of the public but is strongly protected by the support of his members. This is the Corbyn catch-22. This is the Gordian knot that binds the Labour party. There is no sign yet of someone bearing a sword powerful enough to cut through it.