Britain will face an exponentially growing death rate from Covid-19 within weeks unless urgent action is taken to halt a rapidly spreading second wave of the outbreak, the country's senior medics said on Monday.
The United Kingdom already has the biggest official Covid-19 death toll in Europe - and the fifth largest in the world - while it is borrowing record amounts in an attempt to pump emergency money through the damaged economy.
But new Covid-19 cases are rising by at least 6,000 per day in Britain, according to week-old data, hospital admissions are doubling every eight days, and the testing system is buckling.
Chris Whitty, the government's chief medical officer, and Patrick Vallance, its chief scientific adviser, cautioned that if left unrestricted the epidemic would reach 50,000 new cases per day by mid October in the United Kingdom.
"If this continued along the path...the number of deaths directly from Covid ... will continue to rise, potentially on an exponential curve, that means doubling and doubling and doubling again and you can quickly move from really quite small numbers to really very large numbers," Whitty said.
"If we don't do enough the virus will take off and at the moment that is the path that we are clearly on and if we do not change course then we're going to find ourselves in a very difficult problem."
The virus is spreading across all areas of the country and less than 8% of the population have antibodies to the virus, though in London around 17% of the population may have antibodies, Vallance said.
Wales and Scotland
Speed and action are urgently needed, Vallance and Whitty said, adding that as winter was approaching the Covid problem would haunt Britain for another six months at least.
Prime Minister Boris Johnson is due to speak on Tuesday.
Health Secretary Matt Hancock said the restrictions would be different to last time. The government wants to crack down on socialising but schools and many workplaces will stay open.
Semi-autonomous governments in Scotland, Wales and Northern Ireland have directed much of the response to the pandemic in those areas.
Wales slapped curbs on four more areas - Blaenau Gwent, Bridgend, Merthyr Tydfil and Newport - from 1700 GMT on Tuesday, leaving just under a third of the Welsh population under restriction.
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.
"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," Sturgeon said.
The official UK death toll stands at 41,777 people.