Thousands of lives would have been saved if Boris Johnson had imposed a short lockdown when experts recommended it in September, a top scientist has said.
Professor Andrew Hayward said the move would also have "inflicted substantially less damage" to the economy than the new national lockdown for England, which will be imposed on Thursday.
The Scientific Advisory Group for Emergencies (Sage) recommended on September 21 that a shorter "circuit-breaker" lockdown was needed.
Prof Hayward, who sits on the Government's New and Emerging Respiratory Virus Threats Advisory Group, which works with Sage, acknowledged "we can't turn back the clock" on imposing restrictions.
"But I think if we had chosen a two-week circuit-break at that time, we would definitely have saved thousands of lives," he told BBC Radio 4's Today programme.
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"And we would clearly have inflicted substantially less damage on our economy than the proposed four-week lockdown will do."
Chancellor Rishi Sunak said it is his "expectation and firm hope" that England will exit the second shutdown on December 2, but ministers are unable to guarantee that.
The Prime Minister will use a statement in the Commons later on Monday to say that "we will seek" to ease restrictions back into the local tiered system next month.
He will warn that Covid-19 deaths over the winter could be twice as high as during the first wave without the move.
Despite the grim predictions, several senior Conservatives likely to rebel against the Government.
There is anger over the severity of the restrictions, the length they will be needed for and over the delay to imposing them.
From Thursday people in England will not be able to go to pubs, restaurants or gyms.
They are also being advised to work from home if they can.
The new measures were outlined by Boris Johnson at a press conference on Saturday.
Among a raft of statistical analysis delivered at the start of the conference was the prediction that as many as 4,000 people could die of Covid-19 each day in England alone.
The grim figure came from research conducted by the University of Cambridge.
However, more recent data published before the press conference by the university forecasts much lower death rates.
The 1,000 deaths a day scientists warned would be suffered now was revised down to 240 - far closer to the 260 deaths suffered each day on average last week.
The original number was around four times higher than the actual amount of deaths endured.
