THERESA May’s de facto deputy has hit out at hard-line Brexiteers and launched a heartfelt defence of the Prime Minister’s “resilience and strength of character” as her leadership teeters on the brink.

Cabinet Office Minister David Lidington insisted Tory rebels plotting her downfall “haven’t got a better alternative plan available” and should rally behind her in the national interest.

He also challenged Nicola Sturgeon to put “living standards and prosperity in Scotland first” and back Mrs May’s draft Brexit divorce deal, insisting EU leaders had made clear there is no appetite for renegotiation.

Speaking to the media in Edinburgh, Mr Lidington said: “I think anybody who works closely with the Prime Minister, as I do, learns what an absolutely backbreaking job that is.

“With each day that passes, even more this week, I am so impressed with the Prime Minister’s resilience and her strength of character.

“I sometimes wonder what it is that makes her get up in the morning and come in and face the disobliging headlines and cartoons.

“And actually what it is, I know her down to sitting in meetings with her and talking to her, it’s a very old fashioned sense of public service and public duty.

“She’s not somebody who goes in for grandstanding, showboating for media opportunities, she’s there for very decent, old-fashioned sense of public duty.

“And I would say to people who are plotting against her – this is a woman who is intensely patriotic, intensely dutiful who is doing her utmost for families and businesses in every corner of this country.

“They haven’t got a better alternative plan available to the one that she has worked on, and they should rally behind her because that’s what the national interest asks of them.”

The Prime Minister has faced mounting speculation about her future after key figures, including Brexit secretary Dominic Raab, dramatically quit her Cabinet because they could not support the proposed withdrawal deal.

Meanwhile, several Tory MPs have submitted letters of no confidence in Mrs May, with sources now indicating the number sent to Sir Graham Brady, the chair of the backbench 1922 Committee, may be nearing the 48 needed to trigger a leadership challenge.

Mr Lidington laughed off suggestions he is being lined up as a “caretaker” Prime Minister if Mrs May is forced out, adding: “I think that anyone who has seen what being Prime Minister involved is quickly cured of any ambition in that direction.”

The Cabinet Office Minister also moved to reassure Scottish Tory MPs concerned about plans to avoid a hard border on the island of Ireland.

Scottish Tory leader Ruth Davidson and Scottish Secretary David Mundell previously threatened to resign if Northern Ireland was treated differently to the rest of the UK – fearing it could undermine the Union and boost Scottish independence.

Mr Lidington said “backstop” proposals which would see Northern Ireland more closely aligned with EU rules had “always been conceived as an insurance policy only” and there was a determination they wouldn’t be implemented.

But he rebuffed SNP calls for Scotland to receive similar treatment, adding: “I think that the history of Northern Ireland – the fact that there is still a fragile peace building process after decades of bitter and bloodthirsty conflict, means that there is a special circumstance that applies in Northern Ireland.

“And that land border – the only land border the UK has with any other country in the EU – has both an economic but also a real political and talismanic significance that doesn’t apply anywhere else.

“It’s a mixture of the practical and the political that is at work here.”

Mr Lidington called on the First Minister to support Mrs May’s deal to protect jobs and the economy.

He said: “I think there will be an important choice for the Scottish Government and for Scottish members of parliament at Westminster.

“Employers in all sectors want a deal, and they want the stability and the certainty and the clarity that that will bring.

“And I hope very much that, despite the political differences that do exist, and which I respect, that the First Minister will in the end decide to put the interests of Scottish business and living standards and prosperity in Scotland first and support this deal.

“We, for our part, will continue to listen to the views of the Scottish and Welsh governments, to engage with them as we have been doing in recent days, weeks and months and to ensure that their interests are represented and defended in negotiations.”

He said Ms Sturgeon had refused to meet him during his visit to Edinburgh – a claim the First Minister branded “outrageous”.

She said her office was given short notice and she “wasn’t prepared to cancel my constituency commitments at such short notice for the Scottish Government to yet again have to hear empty platitudes rather than be listened to”.