Rishi Sunak has presented a £17bn tax giveaway as the centrepiece of the Conservative manifesto, an offer that was immediately condemned for being “implausible” and mainly benefiting wealthier voters. The policy programme set out by the prime minister, seen by many Tory MPs as probably the party’s last big chance to win over voters, contained few big surprises and was centred on cuts to national insurance and stamp duty, higher thresholds for child benefit and help for pensioners. Launching the manifesto at Silverstone racetrack in Northamptonshire, Sunak accepted he faced an uphill task in convincing voters, not least after his early departure from D-day commemorations last week. “I’m not blind to the fact that people are frustrated with our party and frustrated with me,” the prime minister said. But in cutting taxes, he added, “we are the party of Margaret Thatcher and Nigel Lawson, a party, unlike Labour, that believes in sound money”. However, with the tax cuts costing £17.2bn a year by 2029-30 and much of the money coming from cracking down on tax avoidance and slashing the welfare bill by as-yet uncertain means, thinktanks warned there was a big risk the sums would not add up. Hours after Sunak launched the manifesto, Labour produced its own costings, which predicted a £17.4bn annual shortfall by the end of the parliament. Rachel Reeves, the shadow chancellor, said Sunak was “cosplaying Liz Truss” and risked sparking another rise in mortgage rates. Launching the manifesto to an audience including almost all the cabinet, Sunak announced another 2p cut to national insurance contributions (NICs) and the gradual abolition of all NICs for self-employed people. While some Tory MPs had hoped to reset a faltering election campaign with a bolder policy, for example abolishing inheritance tax, the cuts come on top of other expensive promises, including nearly £6bn annually to increase defence spending to 2.5% of GDP. After the manifesto was announced, some Tory MPs were despondent. “It’s not going to shift the dial,” one said. Others felt it gave them some material to work with in their local constituencies. Sunak has repeatedly attacked Labour over its spending plans, making the much-criticised claim that this would result in £2,000 of extra taxes a household. However, his tax and spend plans are now coming under significant scrutiny – and some scepticism. Fiscal thinktanks, as well as Labour, were particularly critical of the manifesto’s proposed funding sources for the tax cuts and other spending, including a supposed £12bn saved a year by cutting back on social security payments, and £6bn annually on cracking down on tax avoidance and evasion. Paul Johnson, the director of the Institute for Fiscal Studies, said the manifesto could be characterised as “definite giveaways paid for by uncertain, unspecific and apparently victimless savings”. The Resolution Foundation thinktank said financing the tax cuts was conditional on cuts to social security including potentially up to 40% of the bill for payments for people with long-term ill health, as well as huge cuts to already-impoverished councils and unprotected government departments. “All this raises questions over whether this tax and spend package passes the plausibility test,” it concluded. Both thinktanks also noted that the stated tax cuts would mainly help richer earners, with those on lower wages seeing much of the benefit eroded by frozen thresholds for tax payments. An analysis of the tax changes by the Resolution Foundation said that while the 20% of richest households would gain £1,300 a year on average, someone paid £30,000 would see their tax bill fall by just £170. At a Labour press conference in London, Reeves announced calculations that the party said showed a potential £71bn deficit across the five-year parliament. The likely effect on interest rates could, Reeves said, see an average mortgage-holder pay £4,800 more over five years. Labour aides said Keir Starmer was likely to use this statistic repeatedly when he and Sunak are interviewed by Sky News on Wednesday evening, much as Sunak used the £2,000 statistic when he and the Labour leader debated last week. Reeves said the manifesto plans risked “a second Tory mortgage bombshell”, and undermined Sunak’s claims to be fiscally credible: “He said he was the antidote to Liz Truss. Instead, he’s cosplaying Liz Truss by again doing what the Conservatives did in that mini-budget with £71bn of unfunded commitments.” Labour’s costings do not include the idea of abolishing all NICs. The Tory manifesto said this was the party’s “long-term ambition”, but only “when it is affordable to do so”. Other part-surprises in the 70-page document included a beefed-up promise on migration, in which Sunak said a government “will” halve net arrival numbers, and a promise to build 1.6m new homes over the course of the parliament. On green policies, the manifesto continued to push back against net zero commitments, with one policy including giving the Climate Change Committee, which advises the government on emissions, “an explicit mandate to consider costs to households and UK energy security in its future climate advice”. The manifesto also ruled out any future green levies on bills, or taxes on frequent flyers. Sunak’s language stayed the same on the European convention on human rights, despite pressure from the Tory right to offer stronger hints that the party should promise to leave if it created barriers in deporting asylum seekers to Rwanda. “If we are forced to choose between our security and the jurisdiction of a foreign court, including the ECHR, we will always choose our nation’s security,” he said.