Moving too quickly to reopen society risks losing the gains made so far, experts have said, urging caution about the easing of restrictions on June 21.

Professor Robin Shattock, of Imperial College London, said he was concerned that not enough people were vaccinated, particularly in areas that have high levels of the Indian variant.

“We just need to be careful we don’t unlock too quickly and lose those gains that we’ve got,” he said yesterday at a Royal Society of Medicine webinar.

“If we are talking about a delay, we’re talking about a delay of weeks, not months any more. That could be very significant. I’m not so sure why everybody is absolutely obsessed by fixing it to a date and not fixing it to the data.”

He said that within a few weeks we would be “able to see real data, whether the vaccines we’ve rolled out have prevented an increase, an uptick in hospitalisation due to this new variant”.

If there was anything concerning in the data, Shattock said, “maybe we need to hang on a little bit longer. Just because, once you’ve released everything you can’t go back to that period of waiting for a little bit more data, to have that real confidence.”

Peter Openshaw, professor of experimental medicine at Imperial and a member of the new and emerging respiratory virus threats advisory group (Nervtag), agreed with Shattock’s assessment, adding: “ If you have a burning frying pan in the kitchen, you’re not going to carry on sitting down till after dinner to go and put out the fire.” He said it was important to look for any early markers of rising hospital admissions or severe disease over the next week or two.

The long term would involve “watching the virus throw up new variants and us countering with updating of the vaccines”, Openshaw said, although he added that he hoped Covid-19 might “run out of options”.

Susan Michie, professor of health psychology at University College London and a member of the Sage scientific advisory group and Independent Sage, cautioned that a third wave remained a risk.

Asked why people should be concerned about a third wave, given that the UK was in a different situation to last year with a large-scale vaccine programme, Michie said: “Two reasons: one is the higher transmission, the more mutations and therefore the higher the likelihood of a variant that could undermine vaccination.

“And secondly the issue of long Covid, which is very debilitating. So it’s not just a question of hospitalisation and death, but it’s many, many months of people living in a miserable situation and that’s a hit for the economy too.”

Openshaw branded it “unethical” not to share surplus vaccines with the rest of the world.

He called for the “over-purchasing that we and others have done” to be addressed “so as to reduce transmission, and reduce disease amongst those who will definitely benefit a great deal [from vaccines]”.

Shattock added: “We’ve done incredibly well in the UK with rollout of vaccines but we can’t think of ourselves as fortress UK. We need to get those vaccines rolled out to the rest of the world.”