Professor Ravi Gupta, a member of the New and Emerging Respiratory Virus Threats Advisory Group (Nervtag), said with the UK in the grip of an "early" third wave of Covid-19 infections, ministers should consider pushing back their target of scrapping all Covid measures on June 21 "by a few weeks".
The University of Cambridge academic said there had been an "exponential growth" in the number of cases, fuelled by the more transmissible Indian variant, but the "explosive" impact it could have was currently being masked by the high vaccination rate.
More than 39 million people have been given a first jab and a further 25.3 million have had both doses.
It comes as NHS chiefs warned that the lockdown-induced backlog of treatments for ailments other than Covid mean that even a small increase in the number of coronavirus patients could cause hospitals to be overstretched once again.
When asked about the possibility of a delay to freedom from restrictions, environment secretary George Eustice said nothing could be ruled out.
With both deaths and cases up significantly in the past week, experts are urging the Prime Minister to keep to his "data not dates" approach to easing lockdown.
Between May 24 and 30 there were 60 deaths reported within 28 days of a positive coronavirus test, an increase of 42.9 per cent compared with the previous seven days.
Sunday also saw a further 3,240 lab-confirmed cases in the UK, with the number of cases between May 24 and May 30 – 22,474 – 26.8 per cent higher than the previous seven days.
Prof Gupta told BBC Radio 4's Today programme: "It will probably take longer than earlier waves to emerge because of the fact that we do have quite high levels of vaccination in the population, so there may be a false sense of security for some time, and that's our concern.
"I think the problem is we are not too far from reaching the sort of levels of vaccination that would help us contain the virus and I think that 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."
Leading scientific adviser Professor Adam Finn said a clearer picture was needed of the impact of the easements brought in this month before further relaxations take place.
Since May 17, two households or a maximum of six people from multiple households have been permitted to socialise indoors, including in pubs and restaurants.
Cabinet minister Mr Eustice said the UK Government wanted to monitor the data before making a final decision on whether to go ahead with its June 21 plans to abolish social distancing and limits on socialising south of the border.