She will use her speech to try to strike an optimistic note, and is expected to say: "I passionately believe that our best days lie ahead of us and that our future is full of promise".
His fellow Scottish Conservative MP, Ross Thomson, was among those to greet Mr Johnson at the event. "We have that from Theresa May, I think there are others who would struggle to provide that type of leadership", Gauke said.
The Prime Minister will say that as Britain faces this "moment of opportunity", the Conservatives will always act in the "national interest" and put the needs of hard-working people first.
The former Mayor of London quit Mrs May's Cabinet in July in protest at the Chequers plan and in his speech he urged Tories to persuade the Prime Minister to "chuck Chequers" and return to the hard Brexit blueprint she set out at Lancaster House in 2017. "We need to support the Prime Minister, but we're out to change the policy".
But while Johnson may be holding his fire on the leadership for now, he gave both barrels to May's Brexit plan and set out his vision for the Conservative Party - one that returned to its traditional values of low taxes and a strong police. Calling her strategy desperately wrong and humiliating for the country, Mr. Johnson told the crowd: "This is not pragmatic, it is not a compromise".
Mr Johnson warned that voters would not forgive the party for "bottling Brexit".
He reiterated his call for Britain to leave the EU without a withdrawal deal and negotiate a trade agreement similar to the Canada-European Union Comprehensive Economic and Trade Agreement (CETA).
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On his defenders' performance, the Portuguese said: "They tried, they raised the level of their intensity". We don't have the technical quality to build from the back.
Ranting before MEPs on Tuesday, arch-liberal and federalist Guy Verhofstadt also personally attacked senior members of the Tory Party and rejected proposals from leadership favourite Boris Johnson to extend the Article 50 process. May who recently said the naughtiest thing she'd ever done as a child was run through a wheat field against the wishes of a farmer.
Reports have stated that she now has a 'tickly cough' so it may be a disturbed speech as she tries to hold back the splutters.
Mr Mundell added: "I don't think this is a time to be talking about leadership challenges, it is a time to be supporting our prime minister as she takes forward this incredibly hard task of getting a deal with the EU".
Ms Dugdale is the subject of a defamation action after she branded a tweet Mr Campbell posted about Mr Mundell - who came out as gay in January 2016 - as "homophobic" in a column for the Daily Record.
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Ms. May has held back on criticizing Mr. Johnson, but on Tuesday, she said his speech had made her "cross". "Northern Ireland is part of the United Kingdom", she said.
Johnson, who said that the Northern Ireland backstop should be scrapped, received thunderous applause when he said: "Chuck Chequers".