Leaked last night, the Scientific Advisory Board for Emergencies (SAGE) describes a "worst case scenario" based on random swab testing.
The warning also suggests deaths would peak at around 800 a day in late February and could see 25,000 people in hospital, including 5,000 in intensive care.
Drawn up in late July, it comes as the UK's total deaths rose by a further 310, bringing the toll to 45,365.
It recommended a serious tightening of restrictions to prevent people from mixing outside of their households as in the first English lockdown brought in on March 23.
This would then need to remain in place until March 2021, though scientists told schools could still remain open.
It has now urged Downing Street to take drastic action to bring down the R rate, which is currently at 1.6 in England, and estimated to be above 2 in London.
A different study by the Government's Chief Scientific Adviser Sir Patrick Vallance estimated 120,000 excess deaths during the winter.
The shocking forecast came as Imperial College London estimated close to one million people in Britain have the virus in any one day.
The Imperial College London report says: "We estimate 960,000 individuals are harbouring SARS-CoV-2 virus in England on any one day.
"Whether via regional or national measures, it is now time-critical to control the virus and turn R below one if further hospital admissions and deaths from Covid-19 are to be avoided."
The advisory panel this week advised all of England must be put into Tier 3 by Christmas.
However, the Prime Minister is resistant to introducing any further lockdown, with the Chancellor Rishi Sunak stressing the threat to the economy.
A Downing Street source said: "We all want to see families being able to celebrate Christmas and enjoy the holidays together this year.
"That’s why our regional approach is so important – we must act quickly to introduce further necessary measures that are targeted in areas where prevalence of the virus is highest.
"The most important thing people can do between now and Christmas is to remember how crucial social distancing is to stopping the spread of this virus and following all the local rules in their area."