“We need to be very careful about what happens in the UK. We have very stringent rules in terms of the Food and Drug Administration here, about the number of clinical trials, the timing, the number of people and all the rest,” Ms Pelosi told reporters in Washington.

She added: “My concern is that the UK’s system for that kind of judgment is not on a par with ours in the United States. So if [prime minister] Boris Johnson decides he is going to approve a drug and this president embraces that, that is a concern that I have.”…

The UK Department for Health and Social Care said the UK had “some of the most robust standards for approving new treatments and vaccines in the world”.

They added: “Any vaccine must go [through] clinical trials in line with international standards, with oversight provided by the Medicines and Healthcare products Regulatory Agency, which has vast experience in ensuring the delivery of a safe and effective vaccines.”