London, Dec 19 : British Brexit minister David Frost has resigned from Prime Minister Boris Johnson's cabinet, Downing Street confirmed on Sunday. Frost said he had agreed with Johnson earlier this month to leave his post in January, but because his move had been leaked by British media, he decided to "step down with immediate effect", reports Xinhua news agency. The Mail reported earlier on Sunday that Frost has resigned due to his "disillusionment" with Johnson's government, including the imposition of tax increases and additional Covid-19 restrictions, as well as the staggering cost of "net zero" environmental policies. In the resignation letter published by the Downing Street, Frost said he is confident that Brexit is now "secure," but expressed 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," he said. He also expressed discontent over the stricter measures recently introduced by the government to cope with the Covid-19 pandemic. "You took a brave decision in July, against considerable opposition, to open up the country again. Sadly it did not prove to be irreversible," Frost said. Johnson has triggered "Plan B" amid the rapid spread of Omicron in Britain, including a requirement for millions of people to work from home and mandatory face-mask wearing in a wider range of locations. Frost's departure is considered yet another blow to Johnson, whose leadership has come under attack even from his own rebellious backbench MPs. Earlier this week, 99 Conservative MPs voted against stricter Covid-19 controls announced by Johnson. The legislation paving the way for stricter measures only got through the House of Commons with support from the main opposition Labour Party. It was the biggest backbench rebellion of Johnson's premiership. The Conservatives were also hit by revelations of party workers holding Downing Street parties around last December's festive period when the country was in a strict government-imposed Covid-19 lockdown. Scandals and criticism of Johnson's handling of the pandemic have sent the Conservatives' approval ratings to their lowest level since he became Prime Minister in 2019. The latest polls have put the main opposition Labour Party ahead of the Conservatives. The Conservative Party lost a parliamentary seat in the North Shropshire by-election on Friday, a "safe" seat that the party had held for nearly 200 years. "As if we didn't already know, Lord Frost resigning shows the government's in chaos. The country needs leadership not a lame duck PM whose MPs and cabinet have lost faith in him. Boris Johnson needs to apologize to the public and explain what his plan is for the next few weeks," tweeted Jenny Chapman, Labour's shadow Brexit minister. /IANS