DAVID Mundell has vowed to defend Scotland's place in the UK "until my last breath".

The Scottish Secretary has told Theresa May that he would be prepared to step down if a Brexit deal created a political division down the Irish Sea.

During a rowdy Scottish Questions in the Commons, he underscored the strength of his feeling under questioning from SNP MP Patrick Grady, when he was accused of "presiding over a power-grab".

The Nationalist MP for Glasgow North said: "Scottish Tories...have never wanted the Scottish Parliament to succeed and are using Brexit to undermine it."

But Mr Mundell hit back, declaring: "He and his colleagues want to break up the United Kingdom. I will defend our United Kingdom until my last breath."

He went on: "I make no apology for making absolutely clear that the integrity of the UK is a red line for me and my Scottish Conservative colleagues in any deal on leaving the EU. The position is exactly the same for our Prime Minister.

"I know those on the SNP benches' preference would be a Brexit of the most disruptive kind, which they say is best able to take forward their cause."

Lesley Laird for Labour accused the Secretary of State of "flip-flopping over his threat to resign".

She said: "The Secretary of State claims that protecting the integrity of the UK is the most important thing to him. The invisible man in the Cabinet even got a few headlines for himself this week by flip-flopping over his threat to resign.

"Sources close to him claimed he would resign but he denied it himself yesterday so let's be clear: Yes or no? If there is a deal that creates a border in the Irish Sea and undermines the Union, will the Secretary of State resign?" asked the Shadow Scottish Secretary.

Mr Mundell again stressed that any border down the Irish Sea would not be acceptable to him or his Scottish Conservative colleagues.

Ms Laird claimed the UK Government had "just run out of ideas when it comes to Brexit" as she urged the Scottish Secretary to "support Labour's suggestion for a customs union".

The Kirkcaldy MP said: "If he really wants to protect Scotland's place in the UK and stop a border in the Irish Sea he should back Labour's plan for a customs union, so will he?"

Mr Mundell replied: "What I'm absolutely clear on is whatever kind of Brexit might be achieved the worst possible alternative would be a Labour government for this country."