The UK's chief scientific adviser has said the government was urged to impose full lockdown measures around a week earlier than they were introduced, as he admitted the country's coronavirus outcome has "not been good".
Sir Patrick Vallance made the revelation around the timings of the guidance from the scientific advisory group for emergencies (SAGE), as he suggested many factors would determine how well countries had responded to the COVID-19 outbreak.
He also told the House of Commons science and technology committee that the virus was likely to return "in different waves over a number of years".
And he went on to offer resistance to Prime Minister Boris Johnson's efforts to encourage more people to return to their workplaces, saying he saw "absolutely no reason" why official guidance to work from home should be changed.
Sir Patrick insisted the experts realised "we were further ahead in the epidemic than had been thought" in mid-March as soon as the data was available.
He said SAGE's modelling sub-group saw at that point that the number of days over which COVID-19 cases were doubling had gone down to three.
"That's when the advice that SAGE issued was the remainder of the [lockdown] measures should be introduced as soon as possible," he said.
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"That advice, I think, was given on the 18th of March or the 16th of March."
Full lockdown measures were not imposed in the UK until 23 March.
When asked about the UK's response to the pandemic, Sir Patrick appeared to admit mistakes had been made.
"As (chief medical officer Professor) Chris Whitty has said before, it's very difficult to know where we stand at the moment," he said.
"It's clear that the outcome has not been good in the UK, I think you can be absolutely clear about that.
"It is clear you can see a band of countries that have done less well in the temperate zone.
"Countries that are very well connected internationally, countries that have got population structures of a certain type.
"There are many factors that are going to play in this as we look and say, 'what is it that makes some countries having done worse than others?', and there will be decisions made that will turn out not to have been the right decisions at the time."
He had previously said 20,000 deaths would be a "good result" in the pandemic, but latest figures show the number of people who have died with the disease in the UK has risen to more than double that.
Sir Patrick said the country may soon see the "reemergence" of a coronavirus spike.
"You could argue that is the tail end of the first wave still," he said.
"And I think it is quite probable that we will see this virus coming back in different waves over a number of years.
"All we have done is suppressed the first wave and when you take the brakes off you would expect it to come back."
He explained coronavirus could die down but then start "going round the world and coming back again".
"The classic way people think of a second wave is, when the whole things gone away down to low levels, it comes back again next year.
"Thats the seasonal thing thats been seen with pandemic flu for example in 1918.
"We dont yet know if this is a seasonal virus, but I think there are some pretty strong hints it may well be."