‘Billions of doses’ are already being produced at ten factories across the globe by a consortium led by British drugs firms AstraZeneca, he said.

In an upbeat assessment of how the vaccination programme could unfold, he said: ‘I’d be very surprised if this thing [the pandemic] isn’t very clearly on the way down by late spring, at least in this country… we will get to the stage where there is herd immunity through vaccination.’…

The professor said Britain’s Medicines and Healthcare products Regulatory Agency has already been ‘fantastic’, adding: ‘That’s why we say this is one of the best countries in the world to do clinical trials – we have a well-informed, sensible regulator that makes decisions on the basis of a risk-based analysis, rather than a set of dogmatic rules.’

He said he would ‘be very surprised if they don’t move very fast’ when interim results are submitted. Professor Hill suggested data based on as few as 20 cases of Covid could produce statistically significant evidence that the vaccine is effective – but this may not be enough to get the jab cleared in some countries.