Rishi Sunak has said he can “restore the integrity back into politics” as he began a fightback against the political damage from sacking Nadhim Zahawi as Conservative party chair for breaches of the ministerial code over his tax affairs. The prime minister, answering questions after an NHS-themed address at Teesside University in Darlington, said he had acted “decisively” to dismiss Zahawi on Sunday after receiving the findings of an investigation by his ethics adviser, Laurie Magnus. Magnus’s conclusions meant he was “able to make a very quick decision that it was no longer appropriate for Nadhim Zahawi to continue in government”, Sunak said. “It relates to things that happened well before I was prime minister, so unfortunately I can’t change what happened in the past,” he said. “What you can hold me accountable for is: what did you do about it? What I did, as soon as I knew about the situation, was appoint someone independent, looked at it, got the advice and then acted pretty decisively.” Sunak has now lost two senior ministers – Gavin Williamson resigned after less than a fortnight into the new government – and his deputy prime minister, Dominic Raab, is under severe pressure amid an inquiry into multiple claims of bullying, which Raab denies. Sunak, who entered No 10 pledging to restore “integrity and accountability” after the Boris Johnson era, said his swift action on Magnus’s report demonstrated this was still his mission. “That should give you some confidence that these things matter to me, and that I will take whatever steps are necessary to restore the integrity back into politics, and you can have confidence that the process works,” he said. Earlier, a former health department colleague of Zahawi said there was no need for him to step down as an MP despite his breaches of the ministerial code. The comment by the social care minister, Helen Whately, who was a minister at the health and social care department when Zahawi was in charge of the Covid vaccines programme, comes amid signs of a pushback from Zahawi after he was sacked. Asked if Zahawi “got a fair hearing”, Whately told Times Radio: “I would say so, yes.” In a later interview on BBC Breakfast, Whately rejected the idea that Zahawi should step down as the MP for Stratford-on-Avon. “Nadhim was elected as an MP by his constituents back in the last general election,” she said. “We’re all accountable to constituents. And it’s not that long again until there will be another general election in which voters will again make those decisions.” Sunak’s judgment in reappointing Zahawi has come under question from some Conservative MPs, while others felt that the prime minister, who acted within hours of receiving Magnus’s report on Sunday morning, should have sacked him earlier. The Labour party has written to Sunak about a series of issues connected to Zahawi, including when he first knew about the tax affairs and why he previously said the matter had been settled. “There are serious questions for Rishi Sunak to answer,” the Labour chair, Anneliese Dodds, told BBC Radio 4’s Today programme on Monday. “What did he know about the investigation into Nadim Zahawi, the amount of money he had paid in unpaid tax and the penalty he had to pay? “Why did Rishi Sunak say in parliament that there weren’t questions to be answered about Mr Zahawi’s tax affairs and why do we see our prime minister continuing to prop up such a rogues’ gallery of ministers?” In his letter to the prime minister on Sunday, Zahawi said he would support Sunak as a backbencher, but did not apologise or even explicitly mention the findings of the inquiry into his tax affairs, instead criticising some of the media reporting about his case. In a further sign of Zahawi perhaps believing he has been unfairly treated, unnamed allies of the former Tory chair briefed the Spectator on Sunday about what they believed were inconsistencies in the No 10 case about what Zahawi had told officials about his tax. According to the article, the allies say Zahawi did tell officials about the HMRC investigation and the penalty he subsequently paid when he was made chancellor under Boris Johnson, and that the Cabinet Office was thus “fully in the picture” when he became party chair. Other sources told the Times that a “furious” Zahawi believed he was not given the chance to properly put his case to Magnus, and may publish his own formal response to the sacking.