England’s estimated R number range has increased from 0.8-1.0 to 0.8-1.1, according to SAGE.
It indicates that on average every 10 people infected will infect between 8 and 11 others, meaning cases could still be falling – or even increasing slightly.
The latest growth rate range for the epidemic in England is estimated at -3% to 1%.
"This does not necessarily mean R is definitively above 1 and that the epidemic is increasing, but that the uncertainty means it cannot be ruled out," says government advisory body SAGE.
It come as separate Office for National Statistics data suggested about one in 1,340 people in England had coronavirus in the week ending 8 May.
That marks another week on week fall, with around 40,800 people estimated to have had the virus in total.
The previous estimate was one in 1,180, or around 46,100 people.
Wales also saw a big drop, according to the ONS infection survey, with estimated infections more than halving in a week.
It has the lowest estimate for any UK nation, with about 1 in 4,230 believed to have been infected, or just 700 people.
The previous week’s estimate was one in 2,070, or around 1,500 people in total.
There were also significant falls in Scotland and Northern Ireland.
Scotland’s latest estimate is one in 1,250 people infected (4,200 total); from one in 760 (6,900 total) the previous week.
Northern Ireland’s is one in 1,430 people (1,300 total); from one in 750 (2,400 total).
The ONS infection survey tests people in private households around the country for infection and antibodies and is the largest such survey in the UK.
Seven in 10 adults in England were estimated to have COVID-19 antibodies from a previous infection or vaccination, according to the latest ONS data.
It covers the week starting 19 April, so is likely to now be higher as the vaccine roll-out continues.
It takes between two and three weeks after infection or vaccination for the body to make enough antibodies to fight the infection.
The estimated antibody rate for Scotland, Wales and Northern Ireland was six in 10 people.
The figures come as concerns grow over the India coronavirus variant in the UK, with speculation it could push back June’s final step out of lockdown.
Sky News understands that government advisory group SAGE has agreed that surge vaccinations are needed in the areas where most cases are currently being found, such as Bolton and Blackburn.
The variant of concern has only recently been detected in the UK but cases have risen sharply, with over 1,300 as of 12 May.
Early indications are that it is not any more lethal than the others and that vaccines are still effective.