Headteachers are racing to find temporary classrooms for thousands of children amid a growing building safety crisis that has left ministers under pressure to explain why they were slow to shut buildings in more than 100 schools. With the new academic year due to start next week, Labour demanded an urgent audit of the government’s handling of longstanding safety fears about aerated concrete found in the roofs, floors and walls of hundreds of schools, hospitals and other public buildings. As experts estimated that fixing even the immediate problems in schools with reinforced autoclaved aerated concrete (Raac) will cost the taxpayer at least £100m, there were warnings that thousands of children face home schooling for months, with many more to be taught in temporary buildings for as long as a decade. The schools minister, Nick Gibb, said the tally of 154 schools so far identified with the material was sure to rise. Structural engineers were this weekend fanning out to check for the material, which was used until the 1990s and is now considered “life-expired” and “liable to collapse with little or no notice”, according to the Health and Safety Executive. Investigations could take weeks. On Friday it emerged that schools face immediate partial or total closure in Surrey, Essex, Kent, Bradford, Leicester, Durham, Brixton, Southend, Sheffield, Thurrock, Nottinghamshire, Hampshire, Warwickshire and Cumbria. Many headteachers and estate managers spent the day searching for libraries, marquees and vacant office blocks in which to set up temporary schools. Some schools are choosing to switch to remote learning despite ministers saying this should be a last resort. Priti Patel, the former Conservative home secretary, increased pressure on the government over its handling of the crisis, saying she was “extremely concerned” about the safety risk posed by Raac, present in five schools in her Kent constituency. She said ministers “must act quickly and effectively to address this problem, make our school buildings safe, and respond to the questions and concerns that have been raised”. Ministers have refused to list the affected schools or 34 other public buildings found so far to be affected by Raac. These include 24 hospitals, seven court buildings and four Department for Work and Pensions facilities. Harrow crown court was reportedly forced to shut last week because of the presence of the material. Labour’s shadow education secretary, Bridget Phillipson, called for the education secretary, Gillian Keegan, to answer questions on the crisis in parliament on Monday “to give families and school staff clear assurances that schools are safe”. Dangers with Raac have long been known about in government, and in 2021 the Cabinet Office’s Office of Government Property sent out a formal notice about the material, warning that it was “now life-expired and liable to collapse” with minimal or no notice. Mary Foy, Labour MP for the City of Durham, said she was “utterly appalled” that St Leonard’s school in her constituency was among several told on Thursday it must close when Raac had been found in spring. “That the school has only been informed days before term was due to begin beggars belief,” she said. In Southend, parents of children aged three to 14 with special needs including severe learning difficulties were also only told on Thursday that Kingsdown school would be closed next week. The situation was described as “awful” by Lydia Hyde, a Labour councillor, who said a plan should have been drawn up in March, when the school was first inspected. “It causes a huge amount of chaos for these children. It’s not suitable to put up a marquee in a field,” she said. Facing anger from headteachers and unions, the government meanwhile U-turned on its announcement on Thursday that it would not pay for schools in England to find or erect temporary structures. It will also pay for the costs of repairs, which James Porter, a partner at Rapleys, a building surveying firm that has been checking schools for Raac, said is likely to cost the taxpayer at least £100m, even if the scale of the problem does not grow, as many experts anticipate. “We are very much at the beginning of solving the problem and time is running out before an incredibly serious incident could take place,” he said. Costs could rise significantly if it becomes more economical in the long term to demolish and rebuild. Works at just one school in Sheffield – Abbey Lane primary school – are set to cost £620,000. It remains unclear what caused the Department for Education to order schools to immediately shut any buildings made with Raac, a shift from previous policy that required such action only in high-risk cases. Officials said it was due to “a small number of cases where Raac has failed with no warning”, some very recently. They declined to give the locations, as investigations were taking place, but said this had “reduced our confidence that schools with Raac are safe for use”. Nick Gibb said: “A beam that had no sign … that it was a critical risk and was thought to be safe collapsed.” He said the government was taking a “very cautious approach” and that he would be happy for his nieces and nephews to sit in a classroom propped up by a steel girder. But Labour’s Phillipson said: “Children sat underneath steel girders to protect them from the ceiling falling in – the defining image of 13 years of a Conservative-run education system.” In Essex alone, 50 local authority-maintained schools are reported to have the material. With systems already in place at all but three of them, most will be open as usual. There will be remote lessons at one school. At one Surrey school, toilet blocks are now off limits, which means festival-style toilets are being brought in. The governments in Northern Ireland and Scotland have announced that they are checking schools for Raac. Figures obtained by the Scottish Liberal Democrats showed that the substance was present in at least 35 schools in Scotland. Scotland’s education secretary, Jenny Gilruth, said on Friday evening that councils across Scotland were carrying out assessments, with all expected to report back by next week. Bradford city council said it would take between two and four months to install temporary buildings at two of its schools where Raac was found. East Lothian council in Scotland said it was keeping children who were expecting to move up to secondary school in their former primary schools. They will attend lessons such as science and home economics at the affected school.