But in one of his strongest attacks yet on front-runner Liz Truss, Sunak warned party members of an “act of self-sabotage” that could cost the party the election and to be wary of making big promises spending and the tax cuts it previously had. dismissed as fantasy economics. “I would urge them to be wary of any vision that doesn’t involve hard trade-offs and to remember that if something sounds too good to be true – it probably is,” he said. Simon Clarke, the chief secretary to the Treasury who worked under Sunak, said households could not afford to wait seven years. Clarke, a key Truss ally, said: “Liz will cut taxes in seven weeks, not seven years… People are facing the biggest cost of living crisis for decades and the tax burden is at its highest level for 70 years.” . The former chancellor made the pledge after facing domestic criticism from supporters over his narrative of restraint over the Trust’s tax-cutting ambitions. In the announcement on the day party members will start receiving their ballots, Sunak said he would cut the basic income tax rate to 4 p.m. by the end of the next parliament, which he said would represent the biggest income tax cut in 30 years. Truss – whose campaign won support from Sunak’s replacement as chancellor, Nadim Zahawi, on Sunday night – has said he will cut taxes “on day one” of becoming prime minister. He pledged to reverse the rise in national insurance promoted by Sunak at the Treasury, as well as halt the planned rise in corporation tax next year, another Sunak proposal. Sunak said he would cut income tax by 1% from 2024 – a pledge made as chancellor – but said his first priority was to tackle inflation and get borrowing under control. But on Monday he said he would go further if the Conservatives win re-election in 2024 and cut income tax to £16m – costing around £6bn a year. Sunak called the pledge “the biggest income tax cut since Margaret Thatcher’s government” and said it was a realistic promise in the current economic climate. “I will never cut taxes in a way that just raises inflation,” he said, vowing to “always be honest about the challenges we face.” In a coded attack on Truss, Sunak said the party’s future in power was at risk. “To win this leadership contest without leveling with the world about what comes next would not only be dishonest – it would be an act of self-sabotage that condemns our party to defeat at the next general election and sets us up for a long opposition. “I would urge them to approach any vision that doesn’t involve difficult compromises with caution and remember that if something sounds too good to be true – it probably is.” Sunak’s campaign said the 1p cuts would be paid for by increased Treasury Department receipts through projected economic growth projected by the Office for Fiscal Responsibility. However, the UK is still forecast to have the lowest growth in the G20 – apart from Russia – and the worst growth in the G7 at around 0.5%. A Truss campaign source called the pledge “another U-turn” following Sunak’s previous pledge to cut VAT on energy bills – a policy he rejected in office. “He has also made it dependent on growth first – knowing full well that his corporation tax increases are contractionary,” the source said. “The public and members of the Conservative party can see through these flip flops and twists.” Sunak’s campaign hit back saying it was “not a U-turn” and consistent with his pledge to “keep inflation down, grow the economy and then cut taxes.” Truss will travel to the South West today pledging further deregulation of farming – without elaborating – but also promising a short-term extension of the seasonal worker scheme. MPs backing Sunak have privately expressed fears that he will not have time to regain public momentum before members start voting in the coming days. Although the contest is set to run until September, the majority of members are likely to vote in the next few days immediately after receiving them. MPs polling say they believe the race is much closer than the poll picture so far suggests – YouGov polls of Tory members put Truss more than 20 points ahead of her rival. However, Sunak’s supporters pointed to a poll of Tory councilors by Savanta ComRes which put Truss on 31% and Sunak on 29%. About 32% were still undecided. Subscribe to First Edition, our free daily newsletter – every morning at 7am. BST An MP in a south-east seat said the council vote was “a much better indication of things” and there was a significant amount to play for. “In my constituency Rishi is 60/40 ahead. And he’s loved in the home counties, that’s where the bulk of the membership is, there [the] north there are almost no members at all.’ A senior pro-Sunak MP, who had contacted more than half of their members, said they were struck by the number of undecideds. “The Truss vote is soft and too easily persuaded,” they said, saying MPs needed to do more “old-fashioned, one-to-one lobbying” if Sunak was to stand a chance. Another who had taken part in a poll of his members said the vote was “neck-neck – and very soft”. The MP said: “The YouGov polls are usually accurate – I think Liz will win but I don’t think it’s all over.” Labor said the candidates’ final pledges were emblematic of a culture that “favoured headlines, stunts and division, over practical policy plans”. A spokesman said: “As the polls go down, Conservative members will make their choice, but the sooner the whole country gets it, the better. Britain needs a fresh start with Labour.”