BORIS Johnson has been urged to draw a line under devolution and rule out giving Holyrood any more powers over tax and the economy by his rival for the Tory leadership.

With the former foreign secretary now appearing unstoppable, Mr Hunt’s camp all but conceded defeat by asking Mr Johnson to show restraint in Downing Street.

The SNP said the sight of the two candidates trying to carve up another parliament’s powers showed the Tory party’s “arrogance and disdain for devolution”. 

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Nicola Sturgeon recently revealed Mr Johnson had asked her the day after the SNP tsunami in the 2015 General Election if full powers over tax and spending would “buy off” her party. 

At the time, Mr Johnson was the Mayor of London and had yet to enter the Cabinet.

Recalling their chat at an event in London for the 70th anniversary of VE Day, the First Minister said: “Boris and I walked along together and I think he said something that was along the lines of, ‘So Nicola, full fiscal autonomy – does that kind of buy you guys off?’”

Under full fiscal autonomy, Scotland would have its own Treasury and Holyrood would raise all its own taxes, paying the UK for shared services such as defence and foreign affairs.

Borders MP John Lamont, Mr Hunt’s campaign manager in Scotland, said: “Nicola Sturgeon constantly demands more powers but she’s made a complete shambles of the tax and welfare capabilities she has already. Her anti-business approach has reduced tax revenues, meaning less money for schools and hospitals.

“No Conservative leadership candidate should be comfortable handing Sturgeon more control over taxes when it’s abundantly clear she will use them to hammer Scottish businesses to breaking point.”

SNP MP Pete Wishart said: “The arrogance of the Tory party knows no bounds, and the disdain for the devolution settlement is there for all to see. It’s for the people of Scotland to decide how they are governed – not some Tory party that we didn’t even vote for carving up powers up to suit their own political ends. 

“Of course, what’s most revealing about this bizarre campaign pledge is that the Tories have clearly given up on Ruth Davidson ever replacing Nicola Sturgeon as First Minister. Given their crumbling poll ratings in Scotland, no wonder.”

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Mr Johnson’s Scottish campaign was asked for comment.

Mr Johnson, who is backed three-to-one by Tory party members to become PM according to the latest poll, yesterday insisted he was absolutely serious about pushing ahead with a no-deal Brexit.

Asked if his commitment to the October 31 deadline was a bluff, he told the Sunday Telegraph: “No … honestly. Come on. We’ve got to show a bit more gumption about this.”

He added: “We were pretty much ready on March 29. And we will be ready by October 31. And it’s vital that our partners see that. They have to look deep into our eyes and think: my god, these Brits actually are going to leave. And they’re going to leave on those terms.

“Everybody who says ‘I can’t stand the idea of a no-deal Brexit’, what they really mean is actually they don’t want to leave at all.”

However the problems facing a no-deal Brexit also loomed large yesterday. 
The president of the National Farmers’ Union said no-deal would be “catastrophic” for farming as a whole and could force a mass cull of suddenly unprofitable livestock.

Minette Batters told Sky News’ Sophy Ridge On Sunday that losing access to EU markets in a no-deal would be “socially and economically absolutely disastrous for this sector”.

Using sheep farming as an example, she said there were 15 million breeding ewes in the UK, making it the second largest producer of sheep meat in the world, with 40 per cent of it going to France.

A no-deal Brexit would create an insurmountable “tariff wall”, destroying the export market, while New Zealand lamb continued to be imported here, creating an over-supply in the UK.

“That means you will have many farmers going out of business and, indeed, you would have to look at slaughtering quite a large percentage of the national sheep flock,” she said.

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Meanwhile, Tory MPs opposed to a no-deal said they may try to use a bill being debated today to stop the next PM suspending Parliament to force through an exit on World Trade Organisation terms.

Former attorney general Dominic Grieve said it would be “perfectly legitimate” to use the Northern Ireland Bill that extends the deadline for the resumption of power-sharing.

It is understood Mr Grieve may try to force the Government to make a statement on the bill in October, thereby stopping Parliament from being prorogued. 

He told Radio 5 Live: “Northern Ireland and Brexit go rather closely together. The chances are, if Brexit goes through, a no-deal Brexit, it is going to be the end of Northern Ireland’s union with the United Kingdom, with serious political consequences flowing from it.”

Former Tory minister Sam Gyimah told Sky News he thought “thirty, thirty plus” Tory MPs could try to stop the next PM suspending Parliament to deliver no-deal.

Justice Secretary David Gauke also said he thought a “sizeable” number of Tory MPs would try to block no deal, and that he would quit rather than sign up to it. 

He told the BBC’s Andrew Marr he, therefore, expected to be out of his job long before October 31.

He said: “Assuming that he wins, if Boris’s position is that he is going to require every member of the Cabinet to sign up to being prepared to leave without a deal on 31 October, to be fair to him I can’t support that policy – so I would resign in advance.”

Former leadership contender Sajid Javid yesterday endorsed Mr Johnson, amid speculation the Home Secretary would like to be the new Chancellor. He said Mr Johnson was “better placed” than Jeremy Hunt to “deliver what we need to do at this critical time”.

Mr Javid is expected to use a speech tomorrow to call for an emergency Budget to prepare for a no-deal, saying “trust in our democracy” is at stake if there is a delay past October 31.

Scottish Secretary David Mundell was urged to rule himself out of serving in a no-deal Cabinet after he again warned a chaotic exit would put the Union at risk.

He wrote in the Observer: “Scotland has a First Minister whose only true priority is the pursuit of independent. She poses as a defender of devolution while seeking to destroy it.

“A difficult no-deal Brexit would not only damage the economy, it would fuel Nationalist claims of a UK that is insensitive to Scotland’s needs. The new Prime Minister faces considerable challenges, and the future of the UK is high on the list.”

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SNP MP Tommy Sheppard said Mr Mundell had to back up his words with deeds.

He said: “His previous threats to resign have all proven to be nothing more than hollow words – but he must now go beyond a newspaper column and categorically rule out serving in a no-deal Tory Cabinet.”

Shadow international development secretary Barry Gardiner also said Labour would call a no-confidence motion in the next PM’s government when it looked likely to pass.

He added: “We will call a no-confidence vote when we believe that those Conservative Members of Parliament who have said they would support a no-confidence motion in the Government in order to stop a no-deal are likely to support it.”

Pressed on whether it could happen in the autumn, the Labour frontbencher said: “I don’t know because I can’t read the minds of those Conservative MPs who have said they are prepared to do this.”