NORTHERN Ireland will not have a special single market carve-out in the Brexit deal, David Mundell has insisted, as he signalled any such arrangement would be a resignation matter for him.

The Scottish Secretary said how he and Ruth Davidson, the Scottish Conservative leader, were in “very close contact” with Theresa May and No 10 officials because they regarded the Union as a “very fundamental issue to us and we are not prepared to accept an outcome that challenges the integrity of the United Kingdom”.

He explained: “I couldn’t accept a backstop or the final deal, for example, that left Northern Ireland in a significantly different relationship with the EU than the rest of the UK. We want to ensure we have no hard border in Northern Ireland but we also want to protect the integrity of the UK with no border down the Irish Sea either.”

Mr Mundell was asked if he would he resign if a Northern Ireland carve-out was ever part of the final Brexit deal.

He replied: “I don’t think it’s about making threats; it’s about having clarity of what we are trying to achieve. We are not seeking…that Brexit results in the break-up of our own country. The integrity of the UK is one of the key elements of the type of Brexit deal we are seeking, that’s why the so-called Canada deal isn’t acceptable because the deal on offer is only for Great Britain and not for Northern Ireland.”

When it was suggested the Prime Minister had indeed been considering keeping Northern Ireland in the single market to maintain frictionless trade with the Republic, the Secretary of State dismissed the notion out of hand.

“Most reports in recent days in relation to what is and isn’t being proposed in relation to Northern Ireland are inaccurate. There is no plan for Northern Ireland to be in the single market,” he declared.

However, he pointed out how there were current all-Ireland arrangements such as on energy and agriculture, noting how the Good Friday Agreement allowed for difference from mainland Britain.

Yet he stressed: “Differentiation outwith those parameters is not something we can sign up to because we place huge weight on the integrity on the whole of the UK…

“It wouldn’t have been acceptable to us – it’s not on the table – for Northern Ireland to remain in the single market and the rest of the UK not to be in it. Because it is casting Northern Ireland aside and Northern Ireland is an integral part of the UK. We are one country. We cannot have differential arrangements with the EU,” declared Mr Mundell.

His remarks came after the latest meeting of the Joint Ministerial Committee in Whitehall, in which Dominic Raab, the Brexit Secretary, updated the devolved administrations on the Brexit talks and where the issue of migration post-Brexit was discussed.

Michael Russell, the Scottish Government’s Constitutional Relations Secretary, said the Brexit process was “not a successful venture and it’s not a venture that can do anything other than end in tears”.

He claimed there were “heated” exchanges at the JMC, particularly on migration and Scotland’s demographic timebomb. He suggested it had been a “dialogue of the deaf”.

But Mr Mundell hit back and, while admitting there had been “full and frank” exchanges, noted: “Mike Russell’s definition of ‘dialogue of the deaf’ is: he doesn’t get his way.”

The Scottish Secretary again dismissed the Scottish Government’s demand for immigration policy to be devolved and said: “We’re not going to have a differential policy because some of these challenges in relation to demography and depopulation affect other parts of the UK…What we have got to do is to get a solution to those very specific issues and that’s what I’m looking to achieve.”

He confirmed that a White Paper on immigration would be published before the end of the year, which would allow for flexibility on how Scotland’s demographic challenges could be addressed.