The coronavirus reproduction number, or R rate, is thought to have dropped below 1 after three weeks of lockdown.
According to the latest government figures, the rate for the UK is between 0.8 and 1.0.
In further good news, Sage scientists estimate that the number of new infections is infections is shrinking by between 1% and 4% every day.
It is the first time since December 11 the R rate has been below 1, when the more transmissible variant of the disease first found in Kent began to take hold.
An R number between 0.8 and 1 means that, on average, every ten people infected will infect between 8 and 10 other people.
Scientists advising the government said that all regions of England have seen decreases in the R number and growth rate estimates compared with last week, and R is below or around 1 in every region.
However, they warned that despite the reductions, case levels “remain dangerously high and we must remain vigilant to keep this virus under control, to protect the NHS and save lives”.
“It is essential that everyone continues to stay at home, whether they have had the vaccine or not,” a statement from the SPI-M sub-group of Sage said.
“We all need to play our part, and if everyone continues to follow the rules, we can expect to drive down the R number across the country.”
The R rate is estimated to be at its lowest in London (0.7 to .0.9) and the east of England (0.6 to 0.9), which were placed into the toughest local lockdown, level 4, before Christmas.
The midlands, north-east and Yorkshire and the north-west all appear to still have high rates of the disease, with scientists putting R’s range mostly above 1.
Any value above 1 means that the pandemic is still growing. Last week, reproduction number was estimated to be between 1.2 and 1.3.
The updated R rate for the UK follows almost three weeks of Brits following the most stringent Covid-19 rules, after Boris Johnson followed devolved administrations in Scotland, Wales and Northern Ireland in ordering a national lockdown on January 4.
On Thursday, however, the prime minister said it was “too early” to say whether restrictions would last into summer.
He is expected to hold a Downing Street press conference, with chief medical officer Professor Chris Whitty and the UK’s chief scientific adviser Sir Patrick Vallance, at 5pm on Friday.