Liz Truss has pledged to maintain the so-called triple lock guarantee on pension increases, as she fought back against accusations from Keir Starmer that she is “not in charge” of her government or the country. Downing Street and the Treasury had for days refused to commit to the triple lock, under which the state pension would rise by whichever is the greatest of inflation, average earnings or 2.5%, amid a review of spending by Jeremy Hunt, the new chancellor. But at prime minister’s questions on Wednesday, when the SNP’s Westminster leader, Ian Blackford, asked her about pension increases, Truss said: “I honestly don’t know what he is talking about because we have been clear in our manifesto that we will maintain the triple lock and I am completely committed to it. So is the chancellor.” In Starmer’s exchanges with Truss, the Labour leader made predictable capital out of a deeply bruising week for the PM, in which Hunt, who took over from the sacked Kwasi Kwarteng on Friday, tore up much of her fiscal policy, amid speculation she is about to be deposed. The first question of the session, from the Labour MP Justin Madders, set the tone, asking if Truss would explain “why the chancellor lost his job but she kept hers”. Truss replied: “I have been very clear that I am sorry and that I have made mistakes. But the right thing to do in those circumstances is to make changes, which I have made, and to get on with the job and deliver for the British people.” Starmer began by playfully noting that a new biography of Truss was being written. “Apparently it’s going to be out by Christmas,” he said. “Is that the release date or the title?” Noting the U-turns, including the decision to guarantee only until April a cap on domestic energy bills, rather than for two years as originally planned, Starmer asked: “How can she be held to account when she’s not in charge?” Another question went: “What’s the point of a prime minister whose promises don’t even last a week?” Truss largely dodged any direct questions, instead accusing Starmer of having few policies of his own, and of being closely allied to “militant” striking unions, while highlighting the few remaining elements of her planned tax cuts, such as a reversal of a rise to national insurance. Starmer accused Truss of having “conducted an economic experiment on the British public” with disastrous results on mortgage interest rates. “Working people are going to have to pay £500 more a month on their mortgages, and what’s the prime minister’s response? To say she’s sorry,” Starmer said. “What does she think people would think and say? ‘That’s all right, I don’t mind financial ruin – at least she apologised.’” He added: “The only mandate she’s ever had is from members opposite. It was a mandate built on fantasy economics. And it ended in disaster. The country’s got nothing to show for it except the destruction of the economy and the implosion of the Tory party.” Truss replied, to some cheers from the Conservative benches: “I am a fighter, not a quitter.”