Britain's Brexit minister David Davis and one of his deputies have resigned in a major blow for Prime Minister Theresa May as she tries to unite her party behind a plan to retain strong economic ties to the European Union even after leaving the bloc.
"The general direction of policy will leave us in at best a weak negotiating position, and possibly an inescapable one," Davis said in a letter to May.
British media reported that junior Brexit minister Steve Baker had also stepped down.
The resignations come two days after the cabinet approved the plan in a bid to unblock negotiations with Brussels at a meeting at the prime minister's country retreat at Chequers outside London.
Davis said the plan would "make the supposed control by Parliament illusory rather than real".
He was particularly critical of the proposal for a "common rulebook" to allow free trade in goods, saying this "hands control of large swathes of our economy to the EU and is certainly not returning control of our laws in any real sense".
"I am also unpersuaded that our negotiating approach will not just lead to further demands for concessions," he said, concluding that his post required "an enthusiastic believer in your approach, and not merely a reluctant conscript".
May replied in a letter saying that her Brexit plan "will undoubtedly mean the returning of powers from Brussels to the United Kingdom" and was in line with her commitment to leave the European single market and customs union.
"I would like to thank you warmly for everything you have done over the past two years as Secretary of State to shape our departure from the EU," she said.
A long-time eurosceptic, Davis was appointed two years ago to head up the newly-created Department for Exiting the European Union after Britain voted to leave the European Union in a shock referendum.
He became the public face of Brexit, leading the British delegation in talks with Brussels, although his role had been increasingly overshadowed in recent months as May and her aides took a bigger role in the negotiating strategy.
The 69-year-old had reportedly threatened to quit several times over a perceived lack of firmness in Britain's negotiating stance but had remained strictly loyal to the prime minister in public.
May is due to address parliament later today to explain her plan for Britain to adopt EU rules on goods after Brexit, amid anger from MPs in her own party who want a cleaner break and businesses who say it may still cause economic harm.
Conservative MP Peter Bone said Davis had "done the right thing", adding: "The PM's proposals for a Brexit in name only are not acceptable."
Jacob Rees-Mogg, a leading Brexit hardliner, told Sky News: "This is very important. It raises the most serious questions about the PM's ideas. If the Brexit Secretary cannot support them they cannot be very good proposals." Ian Lavery, chairman of the main opposition Labour Party, said: "This is absolute chaos and Theresa May has no authority left.
May's plan would create a free trade area with the EU for goods, to protect supply chains in areas such as manufacturing, while maintaining flexibility for Britain's dominant service sector.
It is unclear whether Brussels will accept this, after repeatedly warning Britain it cannot "cherry-pick" bits of its single market.
Foreign Secretary Boris Johnson, a leading Brexit supporter, was widely reported to have described the plan as a "turd" before agreeing to support it.
Davis, a sharp operator and a gut-instinct politician, was a "Leave" campaigner in the referendum on Britain's EU membership.
He was well acquainted with the Brussels beat: he was Europe minister between 1994 and 1997 as the European issue tore apart then Conservative prime minister John Major's government.
Born to a single mother and brought up on a public housing estate in London, Davis pursued a career at sugar giant Tate and Lyle.
He also served as a reservist in the Special Air Service, the British army's elite special force unit, before entering politics.
Noted for his love of climbing and flying, his ascent in politics began in 1987 when he was elected to parliament, representing a seat in northern England.
Davis was the front-runner in the 2005 Conservative Party leadership contest, but lost out to David Cameron, shedding momentum after a party conference speech fell flat.
When the Conservatives returned to power in 2010, he never got a government post and spent his time on the backbenches campaigning on civil liberties issues.
After Cameron resigned following defeat in the Brexit referendum, Davis was appointed back in government by May, Cameron's replacement.