Conservative MP George Eustice has quit the government over Theresa May’s promise to allow MPs a vote on delaying Brexit if her deal is rejected.
The farming minister said he would be voting for her deal when it comes back to Parliament next month.
But he feared the PM’s offer of votes on delaying Brexit could lead to the “final humiliation of our country”.
Mr Eustice is a longstanding Brexiteer, who stood as a UKIP MEP candidate before joining the Conservatives.
He is the 14th member of Theresa May’s government to resign over Brexit.
The MP for Camborne and Redruth in Cornwall said he was resigning with “tremendous sadness”.
But in his resignation letter, he said: “I fear that developments this week will lead to a sequence of events culminating in the EU dictating the terms of any extension requested and the final humiliation of our country.”
He added: “We cannot negotiate a successful Brexit unless we are prepared to walk through the door.”
The ex-farmer was a former press secretary to David Cameron – and played a leading role in Mr Cameron’s 2005 Conservative leadership campaign.
His resignation comes after Theresa May’s decision on Tuesday to allow MPs a vote on delaying the UK’s departure from the EU, or ruling out a no-deal Brexit, if they again reject the withdrawal deal she has negotiated with the European Union.
BBC political correspondent Ben Wright said Mr Eustice’s resignation was a symbolic stand against what he thought was a mistake in government policy.
The UK scheduled departure date from the EU is still 29 March – but that could be delayed if Theresa May fails to get her deal through Parliament in a vote she has promised will take place on or before 12 March.
Mr Eustice says in his letter that the government should retain the option of leaving without a deal.
“We must be ready to face down the European Union here and now. The absence of an agreement poses risks and costs for them too,” he says in his resignation letter.