Ministers have been told that a four-week delay to easing all Covid restrictions would probably prevent thousands of hospitalisations, as Boris Johnson prepares to tell the English public they will have to wait up to another month for “freedom day”. The government roadmap out of lockdown earmarks 21 June for the last remaining coronavirus restrictions to be lifted in England, but the prime minister is expected to announce on Monday that the timetable will be pushed back by two to four weeks amid a rapid rise in cases of the Delta variant first detected in India. The Delta variant is rising across the UK, where it now makes up more than 90% of new coronavirus infectious. Public health officials are concerned about the variant because it partially evades vaccines, is at least 40% more transmissible than the Alpha variant first detected in Kent, and appears to double the risk of hospitalisation. Johnson and senior colleagues were expected to make the final decision on Sunday evening, after the conclusion of the G7 summit in Cornwall, with the wider cabinet then set to be consulted. The prime minister will attend a Nato summit in Brussels on Monday before returning to Downing Street to deliver the news. Any delay will infuriate lockdown sceptics on the Tory backbenches, who are concerned about the impact on hospitality businesses and have begun to claim they fear the government will never feel confident enough to lift restrictions. On Sunday, Johnson declined to answer the question of whether the delay could be for more than four weeks. The latest modelling of the Delta variant shared with ministers suggests that even with the rapid rollout of vaccines, the UK will face a third wave of infections mostly among younger people who have yet to receive their immunisations. While many older people are now well-protected from two doses of vaccine, hospital admissions are still expected to rise because not all vulnerable people have had their shots, and some do not mount a robust immune response. Modelling to be released on Monday shows that a four-week pause on lifting the restrictions would probably prevent thousands of hospitalisations as it would keep the brakes on the pandemic – albeit lightly – while more people receive their second shots. A surge in the coming weeks would hit the NHS as emergency departments warn they are already struggling with intense demand. “In terms of emergency admissions, last month was the busiest since the start of the pandemic. We are much busier now in emergency departments than at the peaks of either the first or second wave,” said Dr Raghib Ali, an honorary consultant in acute medicine at the Oxford University hospitals NHS trust. “In other parts of the hospital we are catching up with a lot of elective work because of the backlog, so for both of those reasons it’s a very bad time to have additional pressure from Covid. “Before vaccination, all a delay did was push cases into the future, but we can vaccinate millions of people in those four weeks and that will substantially reduce the size of the peak hospitalisations because of that increased coverage,” he added. About 44% of UK adults are not yet fully vaccinated against Covid and more than 2 million of these are aged 50 and over. At the current rate of rollout, a delay of four weeks would mean another 9 million people could have their second doses. Half of these would have time to produce a substantial immune response by the end of the fourth week. A further 7,490 people tested positive for coronavirus in the UK on Sunday, and a further eight people died, bringing the UK total to 127,904 deaths, according to government figures. The importance of second shots emerged from Public Health England research which found that a single dose of Covid vaccine was only about 33% effective against symptomatic disease caused by the Delta variant. The protection ramps up substantially, to about 81%, with the second dose, but in either case the immune system needs at least two weeks to respond. “There are a couple of things that are happening that should make a big difference in the next few weeks. First of all, vaccinations. Second, and slightly more subtly, schools will be out soon, and every week closer to that means less mixing in schools and more people likely to be off work, both reducing transmission,” said Prof Rowland Kao of the University of Edinburgh. “Both of those things, vaccinations and schools, means that the delay has real benefit right now.” Postponing step four of the roadmap would also give scientists more time to collect data on some of the most crucial questions around the Delta variant. Key among these is how much has the vaccination programme weakened the link between infections, hospitalisations and deaths, given that the Delta variant is so much more transmissible, somewhat resistant to vaccines, and appears to cause more severe illness. “To my mind it’s essential we give ourselves more time to get vaccination rates up,” said Prof Peter Openshaw, a member of the New and Emerging Respiratory Virus Threats Advisory Group that feeds into the Scientific Advisory Group for Emergencies (Sage). “It’s not good enough, where we are. We need more time for vaccinations and more time to see what the severity of the disease is like. If it’s causing double or two and a half times the hospital admissions, we need to understand that better.” Graham Medley, professor of infectious disease modelling at the London School of Hygiene & Tropical Medicine and a member of Sage, said: “The evidence has all gone into government, and I don’t want to comment as anything I say will be seen as a preference or a steer for the decision. “It’s a government decision, quite rightly, how to balance the health and healthcare outcomes with all the other harms that Covid-19 and restrictions bring. The evidence from the epidemiology will all be published and open to scrutiny.”