Researchers at Imperial College London also found that the relationship between COVID-19 infections and deaths is diverging.
The government said free lateral flow tests will be available free starting Friday by mail, from pharmacies and in workplaces.
Boris Johnson is expected to announce a plan to ease coronavirus restrictions in increments, starting by reopening schools in England on March 8.
Britain has vaccinated more than 15 million people with a first dose and 537,715 with a second dose, the fastest rollout per capita of any large country.
The death toll in the United Kingdom has been soaring and now stands in excess of 81,000 -- the world's fifth-highest toll -- while more than 3 million people have tested positive.
Some experts are worried that current vaccines will not be effective against the COVID-19 variant called 501Y.V2.
The prime minister said the country is at "a critical moment," with cases rising rapidly in every part of the country.
The British government's main scientific advisory group said the virus' reproduction rate dipped even before the latest lockdown.
A month-long lockdown is going into effect in England, while four Italian regions, including Milan, designated as 'red zones,' will face a partial shutdown from Friday.