Prof Adam Finn from the Joint Committee on Vaccination and Immunisation, which advises the government on vaccine priority, said the battle with Covid-19 was still ongoing as large numbers of the population remain unvaccinated.

More than 25 million people in the UK have had two doses of a vaccine - but this is just under half of the adult population.

The professor told BBC’s Radio 4 that “there’s vulnerability across the country – the idea that somehow the job is done is wrong.

"We’ve still got a lot of people out there who’ve neither had this virus ... nor yet been immunised, and that’s why we’re in a vulnerable position right now,” he added.

His comments come as the Government receives fresh calls to delay ending Covid restrictions in England on June 21 amid warnings of a third wave.

On Monday, the UK reported more than 3,000 new Covid infections for the sixth day in a row and the UK has seen a slight rise in cases linked to the spread of the Indian variant.

The Indian variant - known as B.1.617.2 - is thought to account for up to three quarters of new cases in the UK and has been linked to a surge in cases in some parts of the country including Bolton.

But Downing Street reiterated that the PM had seen nothing in the data to suggest the plan to ease lockdown restrictions would need to be halted.

A No 10 spokesman added: "We will continue to look at the data, we will continue to look at the latest scientific evidence as we move through June,” the BBC reported.

A final decision on whether restrictions will be lifted will be reached on June 14, it added.

Prof Sir Mark Walport, a member of the government's Scientific Advisory Group for Emergencies told BBC Breakfast that more data was needed over the next two weeks to help the prime minister "make the difficult decision".

He said the data on hospital admissions and case numbers would be key to determining whether to lift restrictions.

Asked whether the UK was entering a third wave of the virus, he said he hoped it wasn't "but it's not impossible".