British Prime Minister Theresa May's leadership is understood to be under fresh pressure after Tory MPs spent almost an hour in a private meeting discussing how to oust her.
Theresa May should leave office once she has agreed a Brexit deal with Brussels and steered it through parliament, according to her former policy chief.
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.
A spokesman for May declined to comment on the report.
Mr Johnson spoke at an Economists for Free Trade event on Tuesday attended by a battalion of Tory Brexit big-hitters including Jacob-Rees Mogg, former Brexit secretary David Davis and his ex-deputy Steve Baker, former party leader Iain Duncan Smith and ex-Defra Secretary Owen Paterson.
With Brexit a little more than six months away, concerns have grown that the sides will not reach a deal because the British Parliament and the governing Conservative Party are divided on what Britain's future relationship with the European Union should be.
The pound fell against the dollar to as low as $1.2994 but later recovered to trade flat at $1.3028.
"The treaty is clear, we have two years to reach an agreement before they leave... in March 2019".
While negotiators still need to resolve key disagreements, the European Union is getting ready to schedule a one-off gathering in mid-November so leaders can formally agree to the terms of the divorce, the sources said.
Michael Gove, May's environment minister and a leading Brexiteer, told BBC radio: "I want to ensure that we get a solid vote, which I'm sure we will, when the prime minister brings back the treaty", adding lawmakers should rally behind May.
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 United Kingdom in a "suicide vest" and handing Brussels the detonator. The rift deepened this week with Johnson comparing May's plan to a "suicide vest" on Britain's constitution. Under Conservative rules, a leadership election is triggered if 15% of Conservative lawmakers, now 48 of its 315 members of parliament, demand a vote of no confidence.
The trade union movement is preparing to throw its weight behind a public vote on the final Brexit deal because of fears the United Kingdom is going to "crash out" of the EU.
"We can vote down the bad Chequers proposals on Monday and support the government in a vote of confidence on Tuesday".
The Brexit European Research Group called for the government to agree "equivalence of United Kingdom and EU regulations" for agricultural products in order to keep the border open, and allow Brussels inspectors into Northern Ireland to check their implementation.