The government’s scientific advisers called for a short lockdown in England to halt the spread of Covid-19 last month.
The experts said in a meeting that an immediate “circuit breaker” was the best way to control cases.
Labour said the advice was ignored but No 10 said it took “robust” action. It comes as the Liverpool region prepares to enter a “very high” Covid alert level from tomorrow, the highest of a new three-tier system.
Most areas of England will be on “medium” alert, with measures such as the rule of six, but areas with local restrictions on household mixing are automatically on “high” alert.
Speaking at a Downing Street news conference, Boris Johnson said retail outlets, schools and universities would remain open in all areas of England.
But at the same press conference, England’s chief medical officer, Prof Chris Whitty, voiced concerns over the impact of the new rules, saying he was not confident the highest tier measures “would be enough to get on top of” the virus without further local restrictions.