BIRMINGHAM, England (Reuters) - Prime Minister Theresa May called on her party on Sunday to unite behind her plan to leave the European Union, making a direct appeal to critics by saying their desire for a free trade deal was at the heart of her Brexit proposals.

Britain's Prime Minister Theresa May walks to the Conservative Party Conference in Birmingham, Britain September 30, 2018. REUTERS/Toby Melville

At the start of what is set to be one of the Conservative Party’s stormiest annual conferences, May’s plans were once again attacked by two former ministers, with her ex-foreign secretary, Boris Johnson, calling them “deranged”.

But she also won strong backing from other Brexit supporting ministers, with trade minister Liam Fox and foreign minister Jeremy Hunt turning their anger against the EU, for “taunting Theresa May, one of the most unfailingly polite people”.

Just six months before Britain is due to leave the EU in the country’s biggest shift in foreign and trade policy in more than 40 years, the debate over how to leave the bloc is still raging in the center-right Conservative Party, and even in government.

May’s already fragile leadership was put under further pressure this month when the EU rejected parts of the so-called Chequers plan. But she put a positive spin on those talks, saying she was ready to consider the EU’s concerns.

“My message to my party is let’s come together and get the best deal for Britain,” May told the BBC in the central English city of Birmingham.

“At the heart of the Chequers plan is a free trade deal, a free trade area and frictionless trade ... Chequers at the moment is the only plan on the table that delivers on the Brexit vote ... and also delivers for the people of Northern Ireland.”

May has shown little sign of shifting away from her Chequers plan, named after her country residence where she hashed out an agreement on Brexit with her ministers in July, despite growing criticism that her proposals offer the worst of all worlds.

Johnson, who quit May’s cabinet after Chequers was agreed, called her plans “deranged” and attacked the prime minister for not believing in Brexit.

He, and the former Brexit minister David Davis, are pushing for a Canada-style free trade deal with the EU - a proposal May says will split Northern Ireland from mainland Britain by making the British province adhere to different customs rules.

Michael Gove, May’s environment minister, dismissed his former Brexit ally’s proposals to leave the EU, which have been dubbed “super Canada”.

“I’m in favor of a super Britain deal,” he told an event on the sidelines of the conference. The prime minister has put forward a proposal, which I support.”

EU TAUNTING “BEYOND THE PALE”

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May’s team had hoped the party’s conference would give her a platform to renew her pledge to help those people who are “just about managing”, trying to pull the focus away from Brexit and on to a more domestic agenda where some party officials fear the main opposition Labour Party is gaining the upper hand.

But her first announcement - for an additional levy on foreign home buyers - did little to reset the conversation, with Sunday dominated again with Brexit, a possible leadership campaign and the prospect of an early election.

The conference has become the chance for those ministers with leadership ambitions to parade in front of the party faithful. Johnson’s successor at the foreign office, Jeremy Hunt, gave a speech that, for some, sent a strong signal of intent.

Johnson’s interview in the Sunday Times in which he said, unlike May, he was a true Brexit believer, was also seen by many to be the start of a campaign for the top job - something that angered some Conservatives who are critical of the former foreign minister.

Ian Lavery, chairman of the opposition Labour Party, said the Conservatives were “clearly too busy fighting amongst themselves and have neither the ideas nor the desire to offer real solutions to the problems they have caused”.

Even though May has stuck to her Chequers plan and on Sunday won at least the outward support of most of her ministers, the EU rubbished some of her proposals at a summit in Austria this month.

“We have a right to expect our EU partners to engage seriously, and with respect, on our shared future relationship,” Fox said. “I’m sure I wasn’t the only one after Salzburg to feel that the taunting of Theresa May, one of the most unfailingly polite people I have ever met, was absolutely beyond the pale.”