Colleagues have compared Sir Keir Starmer to a tank: he powers on, under attack, even when the government seems to be falling apart around him. After a disastrous week when he was outmanoeuvred by his own MPs and forced into humiliating retreat over welfare reform, Starmer was in full tank-like mode on Wednesday, at prime minister’s questions, as he moved inexorably towards the line of fire.

He was oblivious to the plight of Rachel Reeves, his chancellor, on the benches behind him. The 8.30am meeting in Downing Street does not take place on those Wednesday mornings when Starmer is preparing for PMQs. But No 10 had been made aware that “something had happened at home” that morning and Reeves was upset. “In normal circumstances,” I was told by a senior aide, “she would have taken the day off.”

These were not normal circumstances: had Reeves failed to appear in the chamber, after the collapse of the government’s flagship welfare reform programme, speculation about her future would have been even more febrile. She knew that, and so did Starmer.

Reeves was upset about a “personal matter”, but she was also under enormous strain: Britain’s first female chancellor had become a “lightning rod” for much of the dismay and anger directed at the government. Farmers, the business community, the disabled, pensioners, red wall MPs, Blairites – the chancellor had angered them all during her year at the Treasury. She seemed increasingly isolated and was being blamed inside the parliamentary party, even more than Starmer, for the welfare shambles. “A chancellor is at their most exposed when they are taking money away,” Morgan McSweeney, Starmer’s chief of staff, has told colleagues by way of explanation for the troubles of Reeves, whom he supports.

Reeves prides herself on being an “iron chancellor”, austere, unyielding, committed to her fiscal rules and pre-election pledges not to raise taxes on income and VAT or increase employees’ national insurance. She is fearful of the power of the bond market and, as she always says to me, “I don’t want to take risks with people’s mortgages”. She was pleased with how her multi-year spending review had been received. “The spending review was the best day I’ve worked in politics in 20 years,” McSweeney said, “because it was the day we made more announcements on the things we’re doing to change people’s lives.”

Since then, the U-turns on the winter fuel allowance, which Reeves had unliterally removed from most pensioners under instruction from the Treasury during a period early in the parliament when she and other senior ministers had complete autonomy, and the rebellion against welfare reform, had weakened her authority. Worse, they had blown a £5 billion hole in the public finances. And here she was in the chamber, brutally exposed, in all her vulnerability and desperation. It seemed, at first, as if she was already mourning the end of her chancellorship.

Kemi Badenoch had seen what Starmer had not: that Reeves, her eyes swollen as tears rolled down her cheeks, was distressed. Does the chancellor have the prime minister’s full support, Badenoch asked, her eyes shining with malign intent. The tank powered straight into the trap set for him.

Starmer is not a nimble performer or fluent speaker, nor respected for his emotional intelligence and empathy. This was the moment to declare total support for the chancellor, the loneliest politician in Britain. Instead, he made a feeble joke about Badenoch’s precarious position inside her own party. Outside the chamber, McSweeney was being inundated with messages from contacts in business who assumed Reeves had been fired or was due to resign. The markets responded to the spectacle of the chancellor’s misery: the pound weakened and the yield on 10-year government bonds, or gilts, rose by the most in one day since the debacle of Liz Truss’s mini-budget in October 2022.

Starmer was compelled to respond. That evening he gave a BBC interview confirming what he had neglected to do in the chamber: that Reeves would be chancellor “for many years”. The next day they hugged in front of the cameras at the launch of the government’s NHS ten-year plan and Wes Streeting, the health secretary, rallied to her support in a buccaneering speech. The markets stabilised and paradoxically Reeves ended the week strengthened: Starmer’s support for her was now unequivocal and No 10 was briefing that she commanded the full confidence of the markets because of her fiscal rules and authority. You couldn’t make it up.

The past week at Westminster was politics at its most raw and unforgiving and it was deeply revealing about the state of the government and the failings of Starmer’s leadership. Reeves likes to project an image of strength, which leads to a certain coldness in public performance. On numerous occasions, she has said to me: “I have been underestimated all my life.” It’s as if she is continuously trying to fight imposter syndrome and prove her detractors wrong; one of whom, Maurice Glasman, the Blue Labour peer, has dismissed her as a “Treasury drone”.

I first met Reeves, when she was a parliamentary candidate (she was elected in 2010), and even then, Labour people – she was already close to Gordon Brown and Ed Miliband – were talking about her as a future chancellor. As an undergraduate at Oxford, she had the choice of either joining Goldman Sachs or the Bank of England. She chose the latter because she believed her destiny was to enter politics. Over the years, in our many conversations, I’ve always had the sense that Reeves was conflicted or self-divided and had slight class and intellectual insecurities. I’ve written before about this doubleness, what I call Rachel 1 and Rachel 2, the former being the restless economist interested in ideas and political economy and the latter the cautious automaton beholden to Treasury orthodoxy.

She is not a moral missionary like Gordon Brown but is a product of the Labour Party. The party has nurtured and encouraged her, created the conditions for her rise, which is why it hurts her so much to know that members have turned against her, and that fellow MPs direct much of the blame at her for the government’s struggles. They lament what they perceive to be her lack of compassion for pensioners, the disabled and families with more than two children. These charges are unfair and wound Reeves deeply.

Starmer, by contrast, comes from outside the party: as a career lawyer he does not relish the game at Westminster, he is bored by arcane Labour rules and procedures, and he doesn’t even enjoy mixing with MPs, which was why he messed up so spectacularly over welfare reform. The work had not been done, the preparation with MPs not made.

It’s been an appalling week for Labour and No 1o advisers now speak of having reached a “fork in the road”: tax rises will follow in the autumn, the soft left will demand the wealthy are targeted, and Starmer will be urged to tell a more convincing story about the purpose of his government, as if he hasn’t had enough time to have done so already. After the events of recent days, what is clear is that he and Reeves are bound inextricably together: if she fails, so does he. Meanwhile, Angela Rayner, who has emerged unscathed from the debacle, watches and waits, her power enhanced.