Brexit minister Lord Frost has resigned from the UK government over "concerns about the current direction of travel".
In a letter to Boris Johnson, the peer, who led Brexit negotiations, said he hoped the PM would "not be tempted" by "coercive measures" to tackle Covid.
Health Secretary Sajid Javid said Lord Frost was an "outstanding public servant", telling the BBC's Andrew Marr programme that while he disagreed with his remarks, the minister had "resigned out of principle... and we have to respect that".
The Mail on Sunday, which first reported the news, said he handed in his resignation a week ago, partly in disagreement with Covid curbs.
But in his letter to the prime minister, Lord Frost said now the arrangement to exit in January had been made public, he would leave with "immediate effect".
He wrote that Mr Johnson had been "an outstanding leader" during turbulence over Brexit, and the pair had a "close common understanding" on their aims in that area.
But after saying "Brexit is now secure", he added: "You know my concerns about the current direction of travel.
"I hope we will move as fast as possible to where we need to get to: a lightly regulated, low-tax, entrepreneurial economy, at the cutting edge of modern science and economic change."
Lord Frost moved on to his concerns over the government's handling of the virus, saying the country needed to "learn to live with Covid".
"I know that is your instinct too, you took a brave decision in July, against considerable opposition, to open up the country again.
Sadly it did not prove to be irreversible, as I wished, and believe you did too.
I hope we can get back on track soon and not be tempted by the kind of coercive measures we have seen elsewhere."
https://www.bbc.co.uk/news/uk-politics-59714241