Experts tracking the spread of Covid-19 in England say infections may have gone up at the beginning of the current lockdown.
Professor Paul Elliot, who is leading the React study at Imperial College London, suggested the current measures may not be strict enough to see a drop in infections and the reproductive rate – the R.
The study on 143,000 people, who were randomly selected, looked at the prevalence of coronavirus including in people without symptoms.
Infections from January 6 to 15 were 50% higher than in early December, the study found.
Prof Elliott told BBC Radio 4’s Today programme the current R rate – which represents how many people an infected person will pass the virus on to – was “around 1”.
He added: “We’re in a position where the levels are high and are not falling now within the period of this current lockdown.”
He added: “We’re seeing this levelling off, it’s not going up, but we’re not seeing the decline that we really need to see given the pressure on the NHS from the current very high levels of the virus in the population.”
Steven Riley, professor of infectious disease dynamics at Imperial, told Times Radio the study had examined a long enough time period to assess the current lockdown.
“It’s long enough that, were the lockdown working effectively, we would certainly have hoped to have seen a decline,” he said.
He said data from previous lockdowns did show a fall, adding that the current research “certainly doesn’t support the conclusion that lockdown is working”.
On what he expects would happen in the current lockdown, he said: “We would expect a similar plateau, a very gradual increase (of infections), if behaviour stays the same and, if our interpretation is correct, if what we are seeing is kind of the result of the post-Christmas period behaviour.”
Government data shows that the number of new cases of Covid-19 per head of population has been falling in all regions of England.
For example, in London, the rolling seven-day rate as of January 15 stood at 703.7 cases per 100,000 people – down from 1,053.4 a week earlier, and the lowest since the seven days to December 19.
Eastern England is currently recording a seven-day rate of 526.8, down from 763.5 and the lowest since December 20.
The Government said the React study does not yet take full account of the current lockdown measures.
In the study, swab tests suggested 1.58% of all people had the virus in early January, up from 0.91% in December.
London had the highest level in the January period at 2.8%, up from 1.21% in early December.
On Wednesday night, Prof Elliott warned that if Covid-19 prevalence continues to be high “more and more lives will be lost”.
He added: “Our data are showing worrying suggestions of a recent uptick in infections which we will continue to monitor closely.
“To prevent our already stretched health system from becoming overwhelmed, infections must be brought down; 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.”
Mobility data in the study, carried out with Ipsos Mori, suggests movement decreased at the end of December, coinciding with Christmas, and increased at the start of January.
Health and Social Care Secretary Matt Hancock said: “These findings show why we must not let down our guard over the weeks to come.
“Infections across England are at very high levels and this will keep having a knock-on effect on the already significant pressures faced by our NHS and hospitals.
“It is absolutely paramount that everyone plays their part to bring down infections.
“This means staying at home and only going out where absolutely necessary, reducing contact with others and maintaining social distancing.”
Elsewhere, Education Secretary Gavin Williamson has said he hopes schools in England can fully reopen before Easter.
“I would certainly hope that that would be certainly before Easter,” he told BBC Radio 4’s Today programme.
He also told Sky News he intended to give schools and parents a “clear two-week notice period” of reopening.
One of the “key criteria” for reopening schools would be whether the pressure on the NHS was lifting, he added.
“My real focus is making sure that children get back into school at the earliest possible opportunity,” he said.
“Schools were the last to close and schools will very much be the first to reopen.”
Meanwhile, Professor Anthony Harnden, deputy chairman of the Joint Committee on Vaccination and Immunisation (JCVI), told ITV’s Good Morning Britain that the Government is “on track” to hit its goal of reaching 15 million people with vaccines by mid-February.
He said the daily figures on the numbers vaccinated – which showed a dip earlier this week – “are often unrepresentative of the overall trend”.
He added: “We often get vaccine supplies, for instance, in our own practice midweek and immunise at the end of the week, so I think it’s much better to look at a weekly trend, rather than the daily figure.”
He said the UK is in a “dire situation” at the moment and insisted that delaying the second dose of vaccines by up to 12 weeks is the right thing to do.
The history of using other vaccines has shown that “one dose often offers really good protection”, he said.
He added: “For instance, the HPV vaccine, initially was licensed for three doses; we’re now thinking about giving it as one dose.
“And there are lots of examples of this, it is biologically completely implausible that the protection (from one dose) will suddenly drop off after three weeks.
“And so, from a public health perspective, an emergency perspective, this is the right thing to do.”