Trade unions have demanded a sharp rise in sick pay for people isolating due to a positive Covid test after the Guardian revealed internal government concerns about a rising proportion of false positives which could lead to growing numbers of people being off work without reason. Health officials have warned privately that, as lateral flow device (LFD) tests are rolled out to all adults in England amid falling infection rates, more than three-quarters of positive results in low infection areas could be misleading. In response, the Trades Union Congress on Friday called on ministers to consider increasing the current £96.35 a week statutory sick pay to the level of the real living wage, warning: “Sick pay is not enough to live on.” Since the start of the pandemic statutory sick pay has only risen 50p a week. Since 9 April everyone in England has been able to order twice-weekly LFD tests which can be completed at home in 30 minutes as part of a bid to keep the virus in check as the lifting of the lockdown continues. Public Health England data suggests that for the previous month 18% of positive results checked using laboratory tests were false – meaning more than 3,000 people and their families potentially self-isolated without reason. These tests were mainly carried out in schools, where infection levels were highest, and during a period of higher rates of infection nationally, which means the proportion of false negatives now is likely to be higher. Last week Ben Dyson, an executive director of strategy at the Department of Health and Social Care, told colleagues that someone who gets a positive LFD result in London, which has relatively low levels of infection, has at best a 25% chance of it being a true positive. “False positives lead to more people having to self-isolate,” said the TUC general secretary, Frances O’Grady. “But too many are going without the financial support they need to self-isolate. This has to change. If people can’t observe self-isolation when they need to, the virus could rebound.” The government has said that out of every 1,000 LFD tests, one was likely to be a false positive, but critics of the mass-testing programme point out that, when scaled up, the number of people wrongly self-isolating balloons. Allyson Pollock, a professor of public health at Newcastle University, tweeted that if the government enabled 4m to 5m tests every week that “will generate five thousand plus false positive cases plus all their contacts – so up to 50,000 people isolating unnecessarily per week”. The DHSC said that with about one in three people not showing symptoms of Covid-19, “regular, rapid testing is an essential tool to control the spread of the virus as restrictions ease by picking up cases that would not otherwise have been detected”. The Labour MP Nadia Whittome also raised concerns on Friday about levels of sick pay, citing a government study suggesting infection rates were falling more slowly in poorer areas where people were less likely to be able to afford self-isolation. “More testing won’t work unless people self-isolate when they need to – and many simply require proper financial support to do so,” she wrote in The House magazine. “At the very least, statutory sick pay should be raised to the equivalent of a week’s living wage … Without action, the current situation threatens public health, undermines the progress we have made and makes ending this pandemic harder.” Julie McCulloch, the director of policy at the Association of School and College Leaders, said many school leaders were concerned about the accuracy of lateral flow tests, with pupils at secondary schools in England required to take two tests a week, and called for a review of their use. “False positives are causing significant unnecessary workload and disruption in schools and colleges. Even though a positive result on an LFD can now be overridden by a negative result on a follow-up PCR test, schools and colleges are still required to act as soon as they receive a report of a positive LFD result,” McCulloch said. Jules White, the headteacher of Tanbridge House secondary school in West Sussex and a leader of the WorthLess? school campaign group, said: “After so much, much lost time, it’s imperative that testing is reliable. We can’t have pupils and staff missing yet more time unnecessarily. I would like to see schools having immediate access to PCR testing and results, in order to verify all positive lateral flow cases. This is especially important for students in years 11 and 13 who are still striving so hard to get the exam grades that they deserve.” A government spokesperson said: “There is a comprehensive package of financial support in place for workers who need to self-isolate to help stop the spread of coronavirus – including a £500 payment for those on the lowest incomes who have been contacted by NHS test and trace. Many employers pay more than the minimum level of statutory sick pay and employers with up to 250 staff can be reimbursed the cost of up to a fortnight’s statutory sick pay.” The acceleration of lateral flow testing comes as rates of infection continue to fall across the UK with new weekly figures on Friday showing that in England one in every 480 people had Covid, down from one in 340 the week before. The latest rates for Scotland, Northern Ireland and Wales are one in 500, one in 720 and one in 920, according to the Office for National Statistics. In late January the rate of infection in England was one in 55.