Who is Lord Frost?
Lord Frost — one of Boris Johnsons' most loyal ministers — has quit his job as Brexit minister in protest over the direction of Tory policy.
But who is the Brexit mastermind that has resigned?
Who is Lord David Frost?
Lord David Frost was appointed as Brexit minister in February 2021.
In September 2020 Boris made Lord Frost a life peer in the House of Lords.
Before that he was the UK's chief Brexit negotiator, having led the UK's Brexit talks with the EU.
He helped negotiate a free trade agreement in the Brexit transition period.
And he was one of the 100 MPs who opposed the Government's decision to implement Plan B Covid restrictions.
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Before that, the Oxford graduate spent more than two decades as a diplomat, from 1987 to 2008.
In 1993, he worked in Brussels as first secretary for economic and financial affairs.
In his first government job he was posted to the British High Commission in Cyprus whilst working for the Foreign and Commonwealth Office.
Lord Frost returned to politics in 2016 as Boris' special adviser after spending five years at the head of the Scotch Whiskey Association.
He then joined the United Nations in New York where he covered Human Rights and Social and Economic Affairs.
Lord Frost also worked as Private Secretary to Sir John Kerr, who was the Head of the Diplomatic Service and as the Economic Counsellor to the British Embassy in Paris in 2001.
And he then became Head of the EU Department and later the Director for the European Union in the Foreign Office before working as the UK's ambassador to Denmark from 2006 to 2008.
Why has he quit?
Sources said the final straw for "Frostie" was last week's bid to impose Covid passports for pubs and big events as well as his growing "disillusionment" with the "direction" of Tory policy.
A Downing Street source said: "This is a proper kick in the balls for Boris and the team.
"Frostie hated the Covid restrictions and higher taxes — but a vaccine passports was the final straw."
Lord Frost resigned from his post as the UK's Brexit Minister after the Government's decisions to go ahead with Plan B Covid restrictions.
What has Lord Frost said?
In a letter to Boris Johnson, the peer, 56, who led Brexit negotiations said he hoped the PM would "not be tempted" by "coercive measures" to tackle Covid.
He has agreed to "step down with immediate effect" as he outlined his "concerns about the current direction of travel".
He said: "I think it is right for me to step down with immediate effect.
"Brexit is now secure...the challenge for government is now to deliver on the opportunities it gives us. You know my concerns about the current direction of travel.
"You took a brave decision in July against considerable opposition, to open up the country again.
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"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."
Boris said he was "very sorry" to have received his resignation.