Professor Chris Whitty and Sir Patrick Vallance will use a live televised address on Monday to deliver a stark message about the consequences of failing to get the coronavirus pandemic under control, amid warnings ministers may be forced to impose national restrictions.
The government’s chief medical officer and chief scientific adviser will warn that second waves of the virus seen in other countries could be replicated in the UK.
Ministers have said the UK is at a “tipping point” in the fight against Covid-19, following fears that deaths could rise to hundreds a day within weeks.
At a briefing in Downing Street, Prof Whitty is expected to say the UK is at a “critical” juncture in the battle against the disease.
He and Sir Patrick will set out a series of potential scenarios if the virus continues to spread. Boris Johnson could also address the country, perhaps as early as Tuesday.
The number of confirmed cases in the UK has risen dramatically in recent weeks, with another 3,899 announced on Sunday.
Londoners are braced for more restrictions in the capital, likely to be announced soon.
Health secretary Matt Hancock said he could not rule out that the capital’s commuters will be told to work from home as soon as this week.
He also refused to rule out further national measures, telling Sky’s Sophy Ridge on Sunday programme: "We have a choice. Either everybody follows the rules — the rule of six and the need to self-isolate if you have a positive test or if you are contacted by NHS Test and Trace — or we will have to take more measures.”
Ministers are understood to believe that to effectively fight the virus compliance with the current coronavirus rules will have to rise to the “top end of the scale”.
“Now is the moment,” Mr Hancock said. “I’m requesting the help of the British people. We truly have got to do this together.”
He also pointed to Belgium, which he said had seen signs of a second wave but had managed to get the disease under control with greater restrictions on socialising.
He also said he would report on his neighbours if they broke the rules “and everybody should”, in a break with Mr Johnson who last week said he would contact the offenders first.
The warnings came as government officials prepared to meet to discuss potential further restrictions for London.
Mayor Sadiq Khan is pressing ministers to introduce measures in the capital, which he has warned may be just "two or three days" behind Covid hotspots like the northwest of England.
He is due to meet the city’s council leaders on Monday, with recommendations to ministers following that.
On Friday Boris Johnson warned Britain was “now seeing a second wave” of Covid-19.