Sir Jeremy Farrar has been part of the independent Scientific Advisory Group for Emergencies (Sage) since the start of the pandemic.

He said he had left at the end of October so he could focus on his work as director of medical charity the Wellcome Trust.

But in a statement, he warned the crisis was "a long way from over".

Sir Jeremy also said Sage scientists had often had to work "under huge pressure" to provide "vital evidence, and independent, expert, transparent advice".

In his statement confirming he had left Sage, he said: "The Covid-19 crisis is a long way from over, with the global situation deeply troubling.

"The high levels of transmission seen in the UK remain concerning, but I stepped down as a participant of Sage knowing ministers had been provided with most of the key science advice needed over the winter months."

The UK recorded 33,865 Covid cases on Tuesday, with the total number of cases in the past seven days down 10.4% on the previous week.

Deaths are still rising, with 293 deaths within 28 days of a positive test reported.

Sir Jeremy said his focus now had to be on Wellcome, adding: "This includes supporting the international research effort to end the pandemic, ensuring the world is better prepared for inevitable future infectious disease threats, and making the case so the full potential of science is realised to inform and drive change against all the urgent health threats we face globally."

He said it had been "an honour to have joined the hundreds of scientists who have contributed" and thanked Sir Patrick Vallance, the government's chief scientific adviser, and Chris Whitty, chief medical adviser, for their "outstanding leadership".

Labour's shadow health secretary Jonathan Ashworth said: "To lose a heavyweight figure like Sir Jeremy from Sage is a serious blow that reveals the level of concern about the government's mishandling of the pandemic."

Sir Jeremy expressed frustration with the government last year, writing in his book that he had considered resigning from Sage in September 2020 as cases were rising in part due to the newly-opened economy, and the government's Eat Out to Help Out scheme.

He wrote in Spike: The Virus vs The People that he felt in summer 2020 that not enough had been done to plan for the coming winter.

He also lamented the delay in introducing a further lockdown until November 2020, saying: "The absence of a decision is a decision in itself."

A government Office for Science spokesperson said: "We can confirm that Sir Jeremy has stood down from the Covid Sage activation, and thank him for his contribution from the very start of the activation. Sage continues to provide government with independent expert scientific and technical advice."