The lockdown in England has failed so far to suppress coronavirus transmission, according to the latest survey, which indicated a “worrying” possible uptick in infections.

The closely watched React-1 study led by Imperial College London concluded that prevalence of the virus, known as Sars-Cov-2, was “very high with no evidence of decline”. The finding was based on the analysis of 142,900 nose and throat swabs from a representative sample of the English population between January 6 and 15.

The researchers estimated that the reproduction number R, which measures the average number of people one individual infects, was between 0.94 and 1.15, with a central estimate of 1.04 — meaning the rate of infection is rising slowly.

Paul Elliott, one of the co-leaders of the study, said his team would continue to monitor closely data that pointed to “worrying suggestions of a recent uptick in infections”.

Prof Elliott warned that unless infections were brought down, the NHS would struggle to cope. “If prevalence continues at the high rate we are seeing, then hospitals will continue to be put under immense pressure, and more and more lives will be lost.”

The study estimated that 1.58 per cent of the population in England was infected, an increase of more than 50 per cent since the previous round of testing from November 25 to December 3. Prevalence was highest in London, at 2.8 per cent, more than twice the level in the last testing round.

Recent data and scientific modelling have sent mixed signals on the direction of the pandemic in England.

Official daily test results have shown a downward trend this week. At the end of last week two other studies — the Zoe Covid study, based on reports from people with a symptom-tracking app, and an analysis by Cambridge university’s Medical Research Council Biostatistics Unit — concluded that the R number had fallen below 1.

But the Scientific Advisory Group for Emergencies, the government’s advisory panel, put the R for England at 1.2 to 1.3 in its latest estimate, published at the end of last week.

Steven Riley of Imperial College, co-leader of React-1, speculated that there had been a fall in infections during the Christmas and new year period, when most people were at home and social interactions were limited, followed by a rise after the festive season as many people returned to work despite the introduction of the third lockdown in England in early January.

Matt Hancock, health secretary, said the study showed “why we must not let down our guard over the weeks to come”.