Sir Mark, chief scientific adviser to the Government from 2013 to 2017, appeared on BBC Newsnight to discuss Covid cases in the UK. Less than a fortnight after the end of lockdown on July 19, the number of coronavirus cases across the UK has dipped in comparison to the week before.

       While Sir Mark highlighted this “precipitous drop” in cases, the former adviser also warned the pandemic “is certainly not over”.

       He said: “The daily average of the week has dropped by about 33 percent.”

       But Sir Mark added the collapse in cases could be explained by several factors, including the end of the school year and Britons remaining cautious.

       “Testing rates have fallen by about 20 percent,” he added.

       The ex-adviser, who now holds a position at Imperial College London, also believes England has not “yet seen the effect of the relaxation of social restrictions on July 19.”

       When asked about herd immunity, Sir Mark said: “We are not there.

       “Herd immunity of course isn’t absolute, it’s not something that is all or nothing.

       “There is obviously a significant degree of population immunity and of course the most vulnerable are protected against the most severe effects of the infection.”

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       Sir Mark stressed the “great success” of the vaccine rollout.

       He explained how those who have received one dose or are fully inoculated are less likely to suffer from long Covid - and are far less likely to transmit the virus.

       There is concern about the Delta variant and how it may reduce protection for Britons who have received just one jab.

       “A single dose of the vaccine is much less effective against the Delta variant than it was against some of the original variant,” Sir Mark added.

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       July 28 saw 27,734 cases and 91 deaths within 28 days of a positive coronavirus test. The latest data suggests a further 825 people have been admitted to hospital with the virus.

       As of Saturday, 6,021 patients were in hospital, with 848 on ventilators.

       In total, the UK has seen 5,770,928 cases and 129,430 deaths from the virus.