The experts said an immediate "circuit breaker" was the best way to control cases, at a meeting on 21 September.
Communities Secretary Robert Jenrick insisted the government had taken "robust action" that "balanced" the impact on the economy.
But Labour has described the documents as "alarming".
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 for coronavirus restrictions in England.
Every area will be classified as being on medium, high or very high alert under the system. It is not clear what the specific criteria is for each alert level.
Most parts of England are the lowest tier, but Essex has asked to be moved to "high" level restrictions.
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Meanwhile, the latest Office for National Statistics figures showed there were 11,444 deaths registered in the UK in the week to 2 October - meaning coronavirus deaths are doubling every fortnight.
At a press conference on Monday evening, Prime Minister Boris Johnson said 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 briefing, England's chief medical officer, Prof Chris Whitty, voiced concerns over the impact of the new rules, saying he was not confident the "base measures" in the highest tier "would be enough to get on top of" the virus.
"That is why there's a lot of flexibility for local authorities [...] to do significantly more," he said.