DAVID Mundell has warned Boris Johnson a no-deal Brexit could “play into the hands of Nicola Sturgeon” and undermine the Union in a parting shot after his sacking.

The former Scottish Secretary, who opposed Mr Johnson’s entering Downing Street, said the First Minister “craved a no-deal... to cause chaos and boost support for independence”.

Mr Mundell was sacked on Wednesday despite Scottish Tory leader Ruth Davidson advising Mr Johnson to keep him in the post he had held for four years.

Mr Mundell’s replacement, Alister Jack, this week downplayed the risk from a no-deal Brexit after signing up to Mr Johnson’s “do or die” pledge to leave by October 31.

Mr Jack said: “I don’t think a no-deal Brexit would be seriously damaging if we prepare for it properly. I do think there will be bumps along the way.”

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However writing in the Scottish Daily Mail, Mr Mundell made it clear he believed a no-deal was a far more serious threat than Mr Johnson and Mr Jack made out.

He wrote: “By far the most important thing I have to say to the new Prime Minister and Secretary of State for Scotland is this: deliver a Brexit that works for Scotland and the whole of the UK. Do that and the Scotland Office’s core mission - to strengthen our place in the Union - becomes so much easier.

“I have set out my concerns about a no-deal Brexit. During the Conservative leadership contest, I continued to highlight the difficulties it would present, especially for Scotland.

“A disruptive Brexit threatens businesses and plays into the hands of Nicola Sturgeon”.

He said the First Minister had “consistently craved a no-deal Brexit in a bid to cause chaos and boost support for independence.

“The new Prime Minister must work hard to ensure that does not happen. Having listened carefully to everything he has said over the past few weeks, I’m hopeful.”

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Reminding Mr Johnson he had named the Union as his top priority, ahead of Brexit, at the recent Tory leadership hustings in Perth, Mr Mundell indicated he did not wholly trust him.

“I take the Prime Minister at his word, but I made clear I see my role as a backbench MP as holding him to account on his commitment to the Union - and I will not shirk from doing so.”

Mr Mundell, 57, admitted he had “significant” differences with Mr Johnson, felt it “inevitable” he would be ousted from the Scotland Office, and was “saddened” when it came to pass. “Despite my own disappointment, though, I’m not downbeat at all. I’m confident Mr John and Alister Jack will do a good job for Scotland. And I would like to think they have some solid foundations to build upon.”