Lockdown measures will be reviewed around the three-week mark on Monday, Downing Street said, as warnings mounted that it will be too early to ease the restrictions to combat Covid-19.
London Mayor Sadiq Khan echoed ministers in saying the capital is "nowhere near" being able to ease measures, as the World Health Organisation warned leaders to be "very careful".
Boris Johnson, who remains in a stable condition in intensive care, had committed to review if the measures could be eased on Monday, three weeks after he imposed the conditions.
But there had been confusion after Foreign Secretary Dominic Raab, who is deputising for the PM, refused to directly answer questions on when it would take place.
The Prime Minister's official spokesman clarified on Wednesday that the review would take place "on or around" the three-week mark as he urged the public to "stick with it" at the "critical time".
He highlighted the Government's key advisers having made clear it was too early to say when the coronavirus pandemic would reach its peak and it would be safe to ease the restrictions imposed on March 23.
The emergency legislation laid before Parliament three days after the PM's announcement states that a review must take place every 21 days, with the first deadline being April 16.
Meanwhile on Wednesday, Mr Khan warned that London is "nowhere near lifting the lockdown".
"We think the peak, which is the worst part of the virus, is still probably a week and a half away," he told BBC Radio 4's Today programme.
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Former health secretary Jeremy Hunt said evidence from other countries suggests the peak remains "for some time" before a reduction occurs.
"I think it's perfectly reasonable to say that the lockdown is going to need to continue for a while and we don't need to take this decision at the beginning of next week," the Conservative MP told BBC Radio 4's World At One.
World Health Organisation regional director Dr Hans Kluge warned that the "progress" Europe had made so far was "extremely fragile".
"To think we are coming close to an end point would be a dangerous thing to do. The virus leaves no room for error or complacency," he added.
"Any shift in our response strategy, relaxing of lockdown status or physical distancing measures requires very careful consideration."
With the number of cases continuing to rise in the UK, health minister Edward Argar also made clear now is not the time to start easing the restrictions.
"We need to start seeing the numbers coming down and that's when you're in the negative," he told BBC Breakfast.
"That's when you have a sense when that's sustained over a period of time, that you can see it coming out of that.
"We're not there yet and I don't exactly know when we will be."
It followed a similar warning on Tuesday from Mr Raab who said ministers first need to see evidence that the measures are working.
The Government's chief scientific adviser Sir Patrick Vallance said the figures "could be moving in the right direction", but suggested they need another "week or so" before they could be sure.