Rishi Sunak refused to properly fund a school rebuilding programme when he was chancellor, despite officials presenting evidence that there was “a critical risk to life” from crumbling concrete panels, the Department for Education’s former head civil servant has said. After the department told Sunak’s Treasury that there was a need to rebuild 300 to 400 schools a year in England, he gave funding for only 100, which was then halved to 50, said Jonathan Slater, the permanent secretary of the department from 2016 to 2020. Conservative ministers more widely believed building new free schools was a greater funding priority, Slater told BBC Radio 4’s Today programme on Monday, as pupils returned to many schools in England for the new term. “For me as an official, it seemed that should have been second to safety,” Slater said. “But politics is about choices. And that was a choice they made.” Sunak hit back, saying it was “completely and utterly wrong” to suggest he was to blame for failing to fully fund the rebuilding programme. In his first public comments since the crisis escalated over the weekend, the prime minister said “new information came to light relatively recently” and the government “acted on it as swiftly as possible”. Sunak acknowledged “the timing is frustrating” for parents preparing to send their children back to school for the autumn. But he added: “There are around 22,000 schools in England and the important thing to know is that we expect that 95% of those schools won’t be impacted by this.” Questions for ministers are mounting about the row over schools built with reinforced autoclaved aerated concrete (Raac) from the 1950s to 1990s. The education secretary, Gillian Keegan, said it was still not known how many could be affected, and how many might need to close, with engineers still to inspect more sites. Keegan, who said the full list of affected schools would be published this week, said the DfE had taken “a very cautious approach” to the issues, and that parents should be reassured that “the vast majority of children will be going back today”. In a damning interview on Monday morning, Slater said two surveys of Raac in schools had uncovered the extent of work needed to remedy a building method supposed to be time-limited to about 30 years of use, with a risk in some cases of sudden and catastrophic failure beyond this. He said it was “frustrating” the Treasury would fund only between a third and a quarter of the work needed. “With the Treasury, of course, you’ve got a concern that there’s never enough money for everything, but we were able to present really good data,” Slater said. “We weren’t just saying there’s a significant risk of fatality, we were saying [there was] a critical risk to life if this programme is not funded.” While he was permanent secretary, in 2018, a concrete block fell from the roof of a primary school, Slater added, “so it wasn’t just a risk. It was actually starting to happen.” A separate analysis by Labour of the amount spent on schools rebuilding while Sunak was chancellor said it fell from £765m in 2019-20, shortly before he took over at the Treasury, to £560m in 2020-21, and £416m in 2021-22, a fall of 45%. Bridget Phillipson, the shadow education secretary, said: “Rishi Sunak bears huge culpability for his role in this debacle: he doubled down on Michael Gove’s decision to axe Labour’s schools rebuilding programme and now the chickens have come home to roost – with yet more disruption to children’s education.” When questioned on Today about the slimmed-down rebuilding programme, Keegan presented it as a standard to-and-fro discussion over funding between a department and the Treasury, saying Sunak’s department might not have seen the specific plan as good value for money. “There’s always a challenge in terms of putting forward your case for funding, and how much you get,” she said. “And every department will always put forward a case for more than they actually get. What you have to do is demonstrate good value for money.” Following Slater’s comments, the Liberal Democrats said ministers must publish the evidence presented to the Treasury by the DfE. Munira Wilson, the party’s education spokesperson, said: “This bombshell revelation shows the blame for this concrete crisis lies firmly at Rishi Sunak’s door. He slashed funding to repair crumbling classrooms when officials said it needed to be increased. Now children and parents across the country are paying the price for this disastrously shortsighted decision.” Speaking earlier on Sky News, Keegan said the DfE “isn’t strictly responsible for the [school] buildings”, as they are maintained by councils or academy chains, but that it would fund any work from the department’s existing budget. “There will be some where they’ve got quite extensive Raac, so they may close so that we can put temporary accommodation in place,” she said. “Many schools are either looking for alternative accommodation, if they’re within a multi-academy trust or within a local authority, or moving to another classroom, if they’ve got a spare classroom. If it’s across the whole school, then that gets more difficult,” she said.