RUTH Davidson will today dismiss Boris Johnson’s “ideological puritan” approach to Brexit, warning that a failure by the Tories to get a deal with Brussels on EU withdrawal risks a Corbyn government.

The Scottish Conservative leader will lead the backlash to the former Foreign Secretary’s outright dismissal of Theresa May’s Chequers Plan, which he described as “deranged. He is due to outline his alternative Brexit blueprint at a fringe tomorrow lunchtime; his only listed appearance at conference.

Ms Davidson will this afternoon tell the party faithful that as the Brexit talks enter their final phase, Conservatives need to go back to first principles: of country; duty; practicality and delivery.

“The belief that every prudent act is based on accommodation and accord. That the best is the enemy of the good if it stops us improving the outcomes for the country.

“The attitude that listens, eyebrows raised, to ivory-towered schemes of the ideological puritan and replies: aye, right.

“It’s this practical, pragmatic and utterly Conservative approach that will get us through,” the Edinburgh MSP will declare, “because, when the future of our country is at stake, it is essential.”

Ms Davidson will add: “Here’s the truth: we can agree a Brexit deal under the Conservatives or we can risk handing the keys of Downing Street to Jeremy Corbyn.

“I know which one I believe is in the national interest. I stand by the Prime Minister.”

Yesterday at conference, Theresa May’s colleagues rallied behind the Prime Minister in defending her and her Brexit blueprint against the Johnson attack.

Ms Davidson, speaking to the BBC’s Politics Scotland, said: "There's been time over the last two years for debate.

"The former Foreign Secretary was in one of the great offices of state during the time that much of this plan was being constructed and praised it as soon ago as last year.”

The party leader urged her colleagues to get behind the PM, to “give her the space to get the deal done” and called for a “period of silence” from the dissenters.

Her colleague David Mundell urged Mr Johnson to ditch his “super-Canada” trade deal proposal and rally round their party leader.

He told The Herald that any proposal that suggested differential arrangements for different parts of the UK threatened the Union.

“Boris Johnson ignores the fact you would have a differential arrangement for Northern Ireland and that is a fundamental objection to that arrangement as currently set out and, therefore, I could never support that proposal,” insisted the Scottish Secretary.

Mr Mundell stressed that Mr Johnson was not proposing anything new to what he had said before.

“There’s not some super-plan because it’s just the same old. I don’t think that takes anything forward. What he needs to do, if he genuinely has the best interests of the country at heart and wants to achieve Brexit, is to support the PM in her efforts.”

Mr Mundell said he was “disappointed” that his former Cabinet colleague had repeatedly failed to rule out challenging the PM for the Tory leadership, adding: “We have to just get on with the job and not get bogged down in these distractions.”

In the conference hall, businessman Digby Jones, the crossbench peer, dismissed the former Foreign Secretary as an "irrelevant and offensive person" to the delight of many delegates.

Lord Jones criticised Mr Johnson for reportedly used a four-letter expletive when asked about industry concerns around Brexit.

Watched by Mrs May in the audience, the former Labour minister said: "Business is so important that when I heard a former Foreign Secretary f-business, it showed him up for the irrelevant and offensive person he really is."