England could fit an air purifier to every classroom for half the price of the new royal yacht, a move which scientists and campaigners say would significantly reduce the spread of Covid in schools. The move would cost about £140m, according to calculations by the Liberal Democrats. Government sources have said there will be no delay to the start of the school term, despite surging Omicron cases, and that any additional restrictions will not include classroom closures. Schools, however, have said high numbers of teacher absences as a result of self-isolation could mean they are forced to send whole year groups home. The education secretary, Nadhim Zahawi, has called on retired teachers and those who have left the profession to help fill the gaps. The general secretary of the Association of School and College Leaders, Geoff Barton, told the Telegraph that classroom closures could occur if schools had no alternative. “If you have a fixed pool available of those who can teach young people, then the only final resort schools and colleges have is to start thinking about the certain year groups that should be prioritised in the short term,” he said. Government guidance suggests teachers should open external windows and internal doors to improve natural ventilation and schools “should balance the need for increased ventilation while maintaining a comfortable temperature”. Opening windows is likely to be more difficult when schools return in cold January temperatures. The Lib Dem education spokesperson, Munira Wilson, said the government’s advice to use CO2 monitors was less effective because they give information on where more airflow is needed but do not affect the flow itself. Headteachers have also criticised the cost of the government’s preferred supplier for air filters – one of the units, made by Camfil City M, costs £1,170 and a Dyson model costs £424.82. Wilson said schools should not be paying for the units at all. “Failure to act right now will fail our children in the future. The government has a week to solve this, otherwise pupils will be left out in the cold and missing out on vital learning once again,” she said. “Nadhim Zahawi gave a cast-iron guarantee that schools would stay open. Unless he gets a grip on this quickly, he will be adding to the countless broken promises from this Government. Worse still, he will be breaking a promise to all our children.” The German government invested £452m in October 2020 in improving ventilation systems in public buildings, including schools, including upgrading air conditioning systems and air purifiers, described by the then-chancellor Angela Merkel as “one of the cheapest and most effective ways” of tackling Covid spread. New York City has also undertaken extensive ventilation surveys and distributed about 100,000 high efficiency particulate air (Hepa) purifiers.