Ministers need to act early to tackle rising Covid infections, the government’s scientific advisers have warned, saying failure to do so could mean harsher interventions will be required this winter.

On Thursday, daily reported new Covid cases in the UK exceeded 52,000, the highest since July, with 49,298 reported on Friday alongside 180 new deaths within 28 days of a positive test.

Figures from the Office for National Statistics released on Friday show that about one in 55 people in England had Covid-19 in the week ending 16 October, a level last seen in mid-January, and infection levels had increased from the week before in all age groups except 25- to 34-year-olds, where the trend was unclear.

The government has repeatedly said it is not yet introducing its “plan B”, a suite of “light-touch” measures such as advice to work from home, compulsory face masks in some settings and the introduction of vaccine passports.

But documents released by the government’s Scientific Advisory Group for Emergencies (Sage) on Friday show warnings from experts that if action is not taken rapidly as cases rise, harsher measures may be needed later.

“In the event of increasing case rates, earlier intervention would reduce the need for more stringent, disruptive, and longer-lasting measures,” minutes of a Sage meeting held on 14 October record.

The experts say there are many unknowns at play regarding the trajectory of the epidemic this winter, including the rate and degree to which protection from vaccinations wanes, and changes in behaviour. However, the documents from the Sage modelling sub-group add that the earlier measures are enacted, the faster they would be likely to be lifted.

“Similarly, the higher the prevalence and growth rates when measures were introduced, the more rapidly hospital pressures would need to be reduced, and therefore the stricter the measures that would be needed to do so,” the SPI-M-O team says.

The warnings chime with previous comments from the government’s chief scientific adviser, Sir Patrick Vallance, that they should “go hard and go early” in the event of rising cases to avoid a winter surge of Covid.

While the documents stress the importance of vaccination, they suggest plan B measures could be effective.

According to a document from the Sage sub-groups Spi-M, Spi-B and the EMG, “reintroduction of working from home guidance, for those who can, may have the largest impact on transmission out of the potential plan B measures.”

The experts add that making the wearing of face coverings mandatory in certain settings is likely to increase their use.

However, they said it was unclear how big an impact vaccine-only certificates would have.

While the Sage documents suggest hospital admissions for Covid are “increasingly unlikely” to climb above levels seen in January, Covid is not the only pressure facing hospitals this winter, with concerns that other respiratory infections, including flu, could place the NHS under extreme strain.

Modelling by researchers at Imperial College London – based on assumptions including a predicted higher uptake of booster jabs than has occurred – suggests with no further measures there could be about 42,800 more Covid hospital admissions and about 5,300 more deaths by the end of March in an optimistic scenario. However this could reach around 100,300 admissions and 9,900 deaths in a pessimistic scenario.

The Sage experts also say capacity to monitor for variants and explore the potential impact on vaccines is crucial. “There should be no complacency around the risk posed by further viral evolution. Emergence of a variant of Delta or a variant from a different lineage that becomes dominant globally is a very real possibility,” the Sage minutes record.

On Friday, the UK Health Security Agency announced the offshoot of Delta, known as AY.4.2 has been designated a variant under investigation due to it becoming increasingly common in the UK. However, experts have said it is unlikely the variant is the main driver for the rising number of Covid cases seen in England, while the variant does not appear to cause more severe disease, and Covid vaccines do not seem to be less effective against it.

Speaking in a personal capacity, several experts who have advised ministers during the pandemic raised concerns about the government’s current approach.

Dr Ben Killingley, an acute medicine and infectious diseases consultant at UCLH, said he supported taking action.

“My personal sense is that we should be increasing precautions and mitigations – plan B. Things are likely to deteriorate with respect to numbers of cases of Covid and other viruses as we move forward. [It] seems policymakers have not learned that you need to act sooner than you would like to, as Patrick Vallance nicely put it. I think that many of my colleagues have the same view,” he said.

Ravi Gupta, a professor of clinical microbiology at the University of Cambridge, agreed. He said: “Plan B should in my personal view be implemented given the escalating and unacceptable morbidity and mortality we are seeing, in addition pressures on the NHS as we approach winter. However, the effects will take a few weeks to see in terms of hospitalisations and deaths.”