The UK's top government scientists warn the country will have nearly 50,000 new coronavirus cases a day by mid-October if the current infection rate does not drop.
Deaths will also rise to 200 per day by mid-November if the current trend continues unabated, England's Chief Medical Officer Chris Whitty and the UK's Government's Chief Scientific Adviser, Sir Patrick Vallance, said during a nationally televised press conference on Monday morning.
On Sunday the UK recorded 3,899 new COVID-19 cases and a further 18 deaths.
"At the moment, we think the epidemic is doubling roughly every seven days," Sir Patrick said at the briefing held at Downing Street.
"If that continues unabated and this grows, doubling every seven days … if that continued, you would end up with something like 50,000 cases in the middle of October per day.
"50,000 cases per day would be expected to lead a month later, so the middle of November, to 200-plus deaths per day.
"The challenge, therefore, is to make sure the doubling time does not stay at seven days."
He said speed and action was required to avoid exponential growth of the virus
Professor Whitty said there were significant rates of transmission throughout the UK and the coming colder weather would help the virus.
"We should see this as a six-month problem that we have to deal with collectively," he said.
"It's not indefinite and … science will in due course ride to our rescue.
"But in this period of the next six months, I think we have to realise that we have to take this collectively very seriously."
The official UK death toll from COVID-19 stands at 41,777 people, while total confirmed cases are edging towards 400,000.
Prime Minister Boris Johnson is due to speak to leaders of the devolved nations on Monday afternoon and chair an emergency COBRA meeting on Tuesday morning before speaking in the House of Commons where new restrictions could be announced.
Circuit breaker or specific restrictions?
The UK first went into a strict lockdown on March 23 which saw people only allowed outside for shopping for essential goods and to exercise once a day, but since May those restrictions were gradually lifted.
But earlier this month Mr Johnson imposed the "rule of six" for England, which made social gatherings of more than six people illegal, whether it be indoors or outside.
There had been some suggestion that the UK could impose a two-week full lockdown as a "circuit breaker" to stop the spread of coronavirus, but Health Secretary Matt Hancock has said the restrictions will be different to last time, with schools and many workplaces to remain open.
Professor Whitty hinted that people may again be asked to work from home and that social contacts would need to be reduced.
"We have to break unnecessary links between households because that is the way in which this virus is transmitted," he said.
"And this means reducing social contacts whether they are at work, and this is where we have enormous gratitude to all the businesses for example who have worked so hard to make their environments COVID-secure to reduce the risk, and also in social environments."
Wales and Scotland to impose restrictions
The semi-autonomous governments in Scotland, Wales and Northern Ireland have directed much of the response to the pandemic in their own areas, and that looks set to continue.
Wales slapped restrictions on four more areas — Blaenau Gwent, Bridgend, Merthyr Tydfil and Newport — from Tuesday afternoon, leaving just under a third of the Welsh population under some form of lockdown.
The Welsh restrictions prevent people entering the areas without a reasonable excuse, such as education or work.
People will also only be able to meet people they don't live with outdoors.
Scottish First Minister Nicola Sturgeon said that additional restrictions were almost certain to be imposed there.
"I need to be absolutely straight with people; across Scotland additional restrictions will almost certainly be put in place ... over the next couple of days," Ms Sturgeon said.