School leaders have said they are having to weigh up pupil safety against financial stability because their budgets have been stretched to breaking point by the burden of the coronavirus pandemic ahead of full reopening in England this week. Headteachers have been left in a bind by the closure in July of a government support fund that has not reopened in time for the uncertain return of millions of students to classrooms. This year’s school funding of £47.6bn would need an injection of at least £2.38bn if Covid-19 related costs account for as little as 5% of expenditure, according to calculations by the teachers union NASUWT. This is in addition to the large-scale investment in child and adolescent mental health services (CAMHS) that local authorities and academy trusts say they will need. The concerns over funding come as the education secretary, Gavin Williamson, used an open letter to parents in England on Sunday to urge them to send their children to school on Tuesday. Acknowledging that some may have concerns about their children attending for the first time since March, he insisted schools were safe and detailed measures put in place to minimise infection. The health risk posed to children by Covid-19 was extremely low, he said. School leaders who spoke to the Guardian, however, described desperately shuffling budgets, sidelining projects and plans and making do with a fraction of what was required. Paul Gosling of Exeter Road community primary school in Devon said he would have ideally liked to have had a cleaner on site from this week to cover shared spaces, but it would have cost £15,000 at a school whose budget may only just balance by the end of the year after many years of cuts. “I cannot plan to have a cleaner on site if I have no idea if I will be able to claim against the fund, so I am balancing safety against financial stability,” he said. The government’s coronavirus schools fund, which was introduced to cover the exceptional costs associated with the pandemic, closed on 21 July. A notice on its website says there are plans to open a “second claims window” in the autumn. Simon Kidwell, the headteacher at Hartford Manor primary school and nursery in Cheshire said he needed to find £50,000 to cover costs. This was after spending £16,000 to make the school “covid secure,” including £11,500 for the installation of 37 hand-washing stations. Losses included £7,000 in nursery fees, £21,000 for before and after-school care and a £10,000 decline in fundraising because of cancelled events. “The government say that the full opening of schools is their number one priority, however, there are no plans to support schools with additional Covid-related costs for the new academic year,” he said. Rebecca Poole, the headteacher at Hampton High in the London borough of Richmond upon Thames, said: “Our funding is really tight. Our business manager has had to cut back on other parts of our school budget and it was really only because we felt it was an absolute priority and other things will have to be sidelined. “We’ve earmarked £10,000 for laptops needed for remote learning after our IT manager negotiated some deals, but it’s really tricky. I know every budget line and it is literally about taking £500 from one budget line into another to pay. There will be things that we won’t be able to invest in.” NASUWT teachers described budgetary constraints that mean special wipes to clean desks, chairs and other surfaces are already being abandoned and replaced with improvised solutions. Others spoke of problems for schools already in debt getting worse, the burden of having to invest in more IT to prepare for remote learning and costs such as hiring more teachers for smaller classes. “Schools are facing significant additional costs in terms of the provision of PPE, additional cleaning regimes, signage and in supporting changes to the school day. These are not one-off costs but will be additional expenditure that schools will need to continue to find from their budgets while Covid-19 remains in circulation,” said Dr Patrick Roach, the NASUWT’s general secretary. “Many of our members have voiced their concerns to us that their schools will struggle to meet these costs, particularly in the context of years of cuts to education budgets. Schools need to be assured that they will be provided with the additional financial and practical resources they need to remain open without cutting corners on safety.” A Department for Education spokesperson said: “Headteachers, teachers and school staff have gone to enormous lengths to ensure children can get back into their classes safely when the new term starts as it is the best place for their education, development and wellbeing. “Throughout the pandemic, schools have continued to receive their core funding, with this year marking the first year of a three-year £14.4bn total cash boost. Schools have also been able to claim for specific exceptional costs such as additional cleaning required due to confirmed or suspected coronavirus cases, worth up to £75,000 for large secondary schools.” The department said that schools had been eligible to claim for costs incurred between March and July as a result of pressures such as increases associated with keeping schools open over the Easter and summer half term holidays and providing free school meals for eligible children who are not in school. The shadow education secretary, Kate Green, said: “If schools are not given additional resources then children across the country will foot the bill, with resources that should fund their education instead paying for public health measures because the government refuse to do so.”