Britain's Brexit Secretary David Davis has resigned as a government minister, delivering a major blow to Prime Minister Theresa May, according to local reports on Monday.

May has accepted Davis' resignation, according to a statement from her office.

"The general direction of policy will leave us in at best a weak negotiating position, and possibly an inescapable one," Davis said in his resignation letter which was published by May's office.

The surprise move came days after May secured her cabinet's support for her Brexit plan on Friday despite claims from the Brexiteer camp that it was "too soft."

Davis, who was appointed Brexit secretary in 2016, was responsible for negotiating Britain's withdrawal from the European Union (EU).

One leading local newspaper, the Daily Telegraph, said Monday his shock decision has plunged May's minority government into a crisis.

Steve Baker, a Conservative MP and Brexit minister in Davis' department also quit the government following May's proposals.

The double blow came as May was preparing to address the House of Commons on the proposals agreed at her day-long meeting with her top ministers on Friday at Chequers, her country retreat.

According to local media, the Brexit proposals promoted by May seek to keep Britain and the EU in a free-trade zone for goods, and commits Britain to maintaining the same rules as the bloc for goods and agricultural products.

The Daily Telegraph said Monday that Davis shocked May by telling her he could not support the Brexit plan agreed at Chequers, prompting speculation that a wave of Cabinet resignations could follow.

The paper said Davis had been on the brink of resigning more than once in recent weeks, but soldiered on because he did not want to risk bringing the prime minister down.

Peter Bone, another Conservative MP, backed Davis' decision, saying that he had done the right thing and it was a principled and brave decision.

"The prime minister's proposals for a Brexit in name only are not acceptable," said Bone.

The Express said the prime minister now faces a major test within the House of Commons and potentially a fractious meeting with MPs and peers on Monday.

May had planned to tell politicians at Westminster that the strategy agreed at her Chequers meeting was the "right Brexit" for Britain.

Speculation was growing in Westminster late Sunday and early Monday that a growing number of supporters of a harder Brexit, who are unhappy with May's proposals, are calling for a leadership challenge.

Britain is scheduled to leave the EU bloc on March 29, 2019. A preliminary agreement was reached between the EU and Britain that the transitional period will last until the end of 2020.