Britain's Brexit minister David Frost has said he was resigning with immediate effect, citing concerns over the "direction" of Prime Minister Boris Johnson's government.
"It is disappointing that this plan has become public this evening and in the circumstances I think it is right for me to write to step down with immediate effect," Mr Frost said in a letter to Mr Johnson which was made public by the prime minister's office.
The Mail on Sunday newspaper had reported details of the resignation earlier tonight.
The paper said that Mr Frost, who led Brexit negotiations with the EU, had handed in his resignation letter to Mr Johnson last week.
But the Mail on Sunday reported he had been convinced to stay on until January.
The newspaper reported it was the introduction of Britain's 'Plan B' coronavirus measures that prompted Mr Frost's decision, including the implementation of Covid passes.
It also said that he had become disillusioned by tax rises and the cost of net zero policies.
Since the newspaper report details emerged, Mr Frost has now resigned with immediate effect.
In his letter, Mr Frost thanked Mr Johnson and said "Brexit is now secure", but he said: "The challenge for the government now is to deliver on the opportunities it gives us. You know my concerns about the current direction of travel."
In his reply, Mr Johnson he was "very sorry" to have received his resignation.
Mr Frost, a supporter of Brexit, has recently been locked in tense rounds of talks with European Commission vice-president Maroš Šefčovič as the UK and the EU attempt to close gaps in post-Brexit arrangements.
The departure of the British government's most senior Brexit negotiator is yet another blow to Mr Johnson who has faced warnings from some of his own MPs that he must improve his leadership or face a challenge.
Mr Johnson said on Friday he took personal responsibility for the loss of a Conservative stronghold in an election defeat that showed public dismay over a litany of scandals and stepped up pressure from mutinous politicians.
DUP leader Jeffrey Donaldson said the departure of Mr Frost is a bad sign for Mr Johnson's commitment to removing the Irish Sea border.
Mr Donaldson said: "Whether on Northern Ireland's access to medicines, our economic prosperity and trade with the rest of the United Kingdom or on the growing divergence between NI and GB, this protocol has been a deeply damaging deal for the people we represent.
"The Prime Minister must now urgently decide which is more important - the protocol or the stability of the political institutions."
Stormont Deputy First Minister Michelle O'Neill said Northern Ireland would not become "collateral damage in the Tory chaos".
She tweeted: "David Frost negotiated Brexit of which a majority here rejected. He has undermined the Protocol since, which limits the damage of Brexit on our people and economy.
"We now need momentum in the talks to make it work better. The North will not be collateral damage in the Tory chaos."
Frost's resignation ends a bad week for Boris Johnson
