Dr Anthony Fauci, the director of the US National Institute of Allergy and Infectious Diseases, warned confidence in the breakthrough jab could be undermined due to how fast it was given the green light.

He mentioned that American regulators would do a ‘more thorough job’, although he later backed away from the comments, saying he was not implying sloppiness on the part of British authorities in whom he had ‘great faith’.

Earlier, he said that Britain ‘kind of ran around the corner of the marathon and joined it in the last mile’ adding: ‘They really rushed through that approval.’

Following Dr Fauci’s comments a spokesperson from the Medicines Health Regulation Authority (MHRA) doubled down on its commitment to the vaccine’s safety.

They said: ‘We have rigorously assessed the data in the shortest time possible, without compromising the thoroughness of our review.

The spokesperson explained that a rolling review of the vaccine data started at the beginning of October and that regulators had made good progress on the review before the last submission of data was received.

‘Any vaccine must undergo robust clinical trials in line with international standards, with oversight provided by the Medicines and Healthcare products Regulatory Agency.

‘No vaccine would be authorised for supply in the UK unless the expected standards of safety, quality and efficacy are met.’ The UK has ordered 40 million doses of the Pfizer jab, enough to vaccinate 20 million people, with 800,000 doses expected to arrive by next week.

Health Secretary Matt Hancock has said he will get vaccinated live on TV to convince people it is safe.

However, Boris Johnson has warned of the ‘immense logistical challenges’ ahead in terms of storing and transporting the jab, with people in care homes expected to face a delay in receiving immunisation from the disease