The coronavirus pandemic could last over 12 months, according to a leaked report to the press.
In an official document, Public Health England also states that nearly eight million people could be admitted to hospital.
The Guardian reported the letter warned health chiefs the epidemic in the UK could last until spring next year and could lead up to 7.9 million people being admitted to hospital.
This is the first time health chiefs have admitted they expect the virus to survive until Spring 2021.
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Boris Johnson is to address the nation on the coronavirus threat after meeting ministers and officials to consider measures including banning mass gatherings and lengthy household isolation for the elderly.
The Prime Minister will chair an emergency meeting of the Cobra committee on Monday afternoon before holding the first of the daily press conferences being planned to update the public on Covid-19.
As the UK death toll reached 35 on Sunday, Health Secretary Matt Hancock said over-70s could be told to stay at home for up to four months within the "coming weeks".
Mr Johnson is expected to discuss the isolation proposal, as well as banning mass gatherings and isolating entire households if one member shows symptoms, during the emergency meeting.
