Grant Shaps, the transport secretary, told LBC radio that the decision to purchase AstraZeneca in such large quantities was taken by the health secretary against the advice of officials.

He said, “We have 100 million doses that someone in the government had, Health Secretary Matt Hancock, common sense to buy in advance – I have to tell you, more than he advised to buy. He was advised to buy 30 million, he decided to buy 100 million.”

Whitehall sources said: “At first, the government was looking at 30 million doses, but the ministers worked to secure a much larger supply.”

Decisions on procurement are made by the Vaccine Task Force Ministerial Committee, which includes the Minister of Health, the Minister of Business, and the Chief Secretary of the Treasury.

A government spokesman said: “The UK was the first country in the world to sign an agreement with the University of Oxford and AstraZeneca to secure early access to 100 million doses of the Covid-19 vaccine.

“The government has fully funded the University of Oxford clinical trials and their candidate was the first to be included in our diversified vaccine suite, which now includes 355 million doses from seven vaccine developers.