Former Brexit minister Steve Baker has said the Conservative Party faces a "catastrophic split" if Theresa May sticks to her Chequers plan for future relations with the EU.
The comments came amid open warfare in the Tory ranks following former foreign secretary Boris Johnson's comparison of the Government's Brexit strategy to placing the UK in a "suicide vest" and handing Brussels the detonator.
Mr Baker, who quit the Government in response to Mrs May's plan to keep the UK in a "common rulebook" with the EU for goods and agriculture, urged the Prime Minister to ditch the policy.
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He said the party's annual conference in Birmingham, starting on 30 September, could prove a decisive moment as Mrs May is forced to acknowledge the scale of grassroots opposition to her proposals.
"If we come out of conference with her hoping to get Chequers through on the back of Labour votes, I think the EU negotiators would probably understand that if that were done, the Tory party would suffer the catastrophic split which thus far we have managed to avoid," he said.
Mr Baker, a former chairman of the influential pro-Brexit European Research Group of Conservatives, urged Mrs May to negotiate a free trade agreement instead of the Chequers plan.
Home Secretary Sajid Javid said a Canada-style deal has a "lot to commend it", but it would not address the problem of the Irish border.
Justice Secretary David Gauke urged the Conservative Party to rally behind Theresa May's Chequers plan for leaving the EU.
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Mr Gauke told the BBC Radio 4 Today programme: "There is an overwhelming majority within the Conservative Party that we respect the referendum result, that we implement it in such a way as to respect the integrity of the United Kingdom and the Good Friday Agreement and ensure that we are in a strong position to grow the economy in the years ahead.
"There isn't an alternative credible plan out there. I think that it is absolutely right that the Cabinet and the parliamentary party backs the Prime Minister. In challenging circumstances she is the right person to deliver the right deal for this country."