The government’s scientific advisers called for a short lockdown in England to halt the spread of Covid-19 last month, newly released documents show.
The experts said an immediate “circuit breaker” was the best way to control cases, at a meeting on 21 September.
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 Wednesday, 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.
A “very high” alert sees pubs and bars close if they do not serve “substantial meals”, almost all household contacts banned and advice against travel.
Speaking at a Downing Street news conference on Monday evening, Boris Johnson said retail outlets, schools and universities would remain open in all areas of England.
The PM added the alert system for England could succeed in driving cases down if it was implemented “very effectively”, and he rejected the “extreme route” of a full nationwide lockdown “right now”.
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.
Released shortly after the press conference, minutes from the meeting of the Scientific Advisory Group for Emergencies (Sage) – which feeds into UK government decision making – stated the advisers had called for the immediate introduction of a short national lockdown three weeks ago.
Of all the measures proposed by the advisory group, just one – advising those who can work from home to do so – was implemented by the government at the time.
In the documents, Sage warned that “not acting now to reduce cases will result in a very large epidemic with catastrophic consequences”.