Adviser and microbiologist Professor Ravi Gupta said the unlocking of restrictions on June 21 should be delayed “by a few weeks” because of a new wave of Covid infections.
“We are not too far from reaching the sort of levels of vaccination that would help us contain the virus,” he told BBC Radio 4’s Today programme.
“People are not saying we should abandon the June 21 date altogether but just to delay it by a few weeks while we gather more intelligence and we can look at the trajectory in a clearer way.
“If you look at the costs and benefits of getting it wrong, I think it is heavily in favour of delay.
“Yes, we will learn to live with it but this date that was set did not take into account the fact we would have a new variant on the horizon, with properties that allow it to evade antibodies to some extent and a virus which is more transmissible.”
Another leading scientific adviser to the government also urged caution, saying authorities ought to have a clear picture of the pandemic before such moves are made.
Professor Adam Finn, from the Joint Committee on Vaccination and Immunisation (JCVI), said while the country’s vaccination programme “will ultimately give us … protection” against the Indian variant, key markers in the community should be taken into account before the next phase of reopening.
“I think it’s unfortunate that everyone’s got this particular date in their head, because really what we need to do is understand how things are going and adjust accordingly,” Prof Finn told ITV’s Good Morning Britain.
“What we’ve done wrong in the past is left it too late and delayed making decisions, ultimately pushed them back and then ended up with large waves of infection.
“This time around, we should be cautious, wait to see what’s happening, and then let everyone free, if you like, once we know for sure that that’s safe and that we can do that without having another round of lockdowns and so on.”
While encouraging data has emerged in recent weeks over Covid hospital admissions in Britain, Prof Finn said any impact on admissions brought by the easing of restrictions in May would not be known for many days yet – “around about June 21 or just before that”.
It comes as Vaccines Minister Nadim Zahawi said that all over 50s will have been offered the second dose of the vaccine ahead of June 21.
Additional reporting by the Press Association.