Experts have cast doubt on the government’s policy of letting large numbers of the British population catch coronavirus in a bid to create "herd immunity", warning it may not work and people could be susceptible to catching it again.

On Friday, the UK’s chief scientific adviser Sir Patrick Vallance said a level of herd immunity – where a significant proportion of people recover and become immune to the infection – was desirable and could protect the public in the event the virus became a seasonal infection.

He told Sky News: “Communities will become immune to it and that’s going to be an important part of controlling this longer term.

“About 60 per cent is the sort of figure you need to get herd immunity.”

But leading scientists and officials warned there is no guarantee people will become permanently immune to the Covid-19 virus, and said it is too soon to know what could happen as the virus spreads through the population.

Dr Nicola Rose, head of virology at the National Institute for Biological Standards and Control, said: “Obviously contain and delay is the approach being taken in the UK and in a number of different countries. The approaches are really to buy time in context of the healthcare system and time for vaccines to be developed.

“We don’t know how the pandemic will evolve. With flu for example it comes and goes in waves. This may well be the case here. We really don’t know whether there will be herd immunity or not.

“As the virus goes through a population, people may start to develop their own immunity. It is early days really with this virus to understand what that looks like. I think we’re a long way from what we would technically call herd immunity.”

She said it would only be after people had been infected and their immune response analysed that the true picture could be established around whether people were immune to further infection.

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Professor Hanneke Schuitemaker, global head of viral vaccine discovery for Janssen Vaccines, said: “We don’t know how long natural immunity will last. And if people who have experienced the infection will be protected forever thereafter or whether we will need vaccines to support them that gives continuous protection against reinfection.”