The UK could see 50,000 new coronavirus cases a day by mid-October without further action, the government's chief scientific adviser has warned.
Sir Patrick Vallance said that "would be expected to lead to about 200 deaths per day" a month after that.
It comes as the PM prepares to chair a Cobra emergency committee meeting on Tuesday morning, followed by a statement in the House of Commons.
On Sunday, a further 3,899 daily cases and 18 deaths were reported in the UK.
Speaking at Downing Street alongside chief medical adviser, Prof Chris Whitty, Sir Patrick stressed the figures given were not a prediction, but added: "At the moment we think the epidemic is doubling roughly every seven days.
"If, and that's quite a big if, but 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.
"Fifty-thousand cases per day would be expected to lead a month later, so the middle of November say, to 200-plus deaths per day.
"The challenge, therefore, is to make sure the doubling time does not stay at seven days.
"That requires speed, it requires action and it requires enough in order to be able to bring that down."