Imported coronavirus variants are unlikely to set lockdown easing back to “square one” because immunity from vaccines “won’t just disappear”, according to a key figure on the UK’s immunisation committee.

Professor Adam Finn, a member of the Joint Committee on Vaccination and Immunisation (JCVI), said he expected a “gradual erosion” of vaccine protection as the virus evolves but not enough to “scupper” the Prime Minister’s road map, as one leading scientist had predicted.

On Friday, Imperial College’s Danny Altmann said “we should be terribly concerned” after 77 cases of a potentially vaccine-busting Covid-19 mutation first discovered in India were identified in Britain.

“They (variants of concern) are things that can most scupper our escape plan at the moment and give us a third wave. They are a worry,” Professor Altmann told the BBC.

Prof Finn said he thought the immunology expert had been “a bit pessimistic” with his assessment.

“We’ve all expected evolution of this virus to occur from the start,” he told Times Radio.

“I also think that we know from other viruses and previous experience that the immunity that vaccines give won’t just disappear.

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“It will be a gradual erosion. It won’t be back to square one. I would be really surprised if that happened.

“So, I think, possibly, that interpretation is a bit pessimistic.”

Prof Altmann said he found it “mystifying” and “slightly confounding” that those flying in from India were not required to stay in a hotel, with the virus soaring in the south Asian country.

India is not currently on the Government’s “red list” for travel, which sees people who have been in those countries in the previous 10 days refused entry to the UK.

British or Irish nationals, or people with UK residency rights, are able to return from red list countries but must isolate in a quarantine hotel for 10 days.

Prof Finn said, with the pandemic “raging” in places such as India – which recorded more than 217,000 cases in 24 hours on Friday – and Brazil, international travel would continue to pose a “problem”.

On Saturday, the global death toll from Covid-19 topped three million, according to the Johns Hopkins University’s count.

“We’re going to need to continue to be really quite careful,” Prof Finn continued, “to avoid moving the virus around, so I think travel won’t go back to normal yet.”

A Downing Street spokesman told reporters that the Government’s red list of travel ban countries is “under constant review”, when asked why India did not feature on it.

No 10 said Mr Johnson’s visit to India “is still happening later this month” but, as already announced this week, would be “slightly shorter” than the initial four-day planned trip, with most of the meetings expected to be shoehorned into a single day.