BORIS Johnson has been accused of performing a “dubious U-turn” by pledging to keep the funding formula that distributes extra spending to Scotland after coming under pressure to do so from Jeremy Hunt.

The move came as both candidates in the Conservative leadership contest seek to emphasise their ironclad Unionist credentials ahead of this Friday’s Scottish hustings in Perth.

Mr Johnson has a history of opposition to the 40-year-old Barnett Formula, saying it produced “deeply inequitable outcomes," and was a "system of amazing political antiquity by which the English taxpayer sends about £20 billion every year to Scotland as a kind of present".

In 2012, he suggested a pound spent in Croydon would generate far more than one spent in Strathclyde and that more jobs would be created in Scotland by investing in London rather than locally, declaring: “If it causes Celtic wailing, then I'm willing to go there and make the case that it's right for them too."

The Hunt camp urged Mr Johnson to “stop dodging questions and follow Jeremy Hunt in committing to the Barnett Formula that underpins the Scottish Budget”.

It warned, without it, Scotland's Budget could be cut severely and Barnett consequentials such as the recent £2 billion extra for Scotland's NHS would be in jeopardy.

"The Barnett Formula is essential to protect Scotland's public services. That's why a government run by Jeremy would maintain it, to help ensure Scotland's schools and hospitals get the funding they need," said a spokesman.

John Lamont, the MP for Berwickshire, Roxburgh and Selkirk, a Hunt supporter, also waded in saying: “Boris is already refusing to debate Jeremy. He shouldn't dodge questions on the Barnett Formula too.

“This shouldn’t even be a difficult question. There is no case for scrapping the Barnett Formula. The only other people who want to get rid of it are the SNP by dividing the UK.

“Boris said it was reckless of David Cameron to commit to keeping the Barnett Formula. The only thing reckless would be scrapping it,” added Mr Lamont.

The SNP intervened with its MSP Tom Arthur accusing Mr Johnson of “threatening to axe the Barnett Formula and slaughter Scotland’s public services” to fund a disastrous no-deal Brexit.

But last night, the Johnson camp insisted there would be “no change” to the funding formula if the former London Mayor won the leadership contest.

A source said: “For the SNP to suggest otherwise shows a hitherto unseen level of desperation and underlines just how much they would fear a Conservative and Unionist Party led by Boris.”

One Conservative insider said Mr Johnson’s move was a “dubious U-turn after he’s spent more than a decade criticising Barnett”.

A Scottish Conservative MP told The Herald: “Boris knows he’s got to be an uber-Unionist now more than ever. He knows he is seen as a London/south-east politician. Both candidates know this is a critical moment for the Union. Boris no longer has the luxury of firing off his blunderbuss; he has to watch his words. In a few days’ time he could become our PM.”

Mr Lamont responded to the Johnson camp’s remarks, saying: “I’m pleased that despite what Mr Johnson has said in the past about reviewing the special funding arrangements for Scotland, he has now apparently u-turned on this policy.

“Jeremy Hunt has always been clear that he supports the continuation of the Barnett Formula; no ifs or buts and no U-turns.”

Earlier, the Foreign Secretary insisted he could deliver a no-deal Brexit while still protecting the Union from a Nationalist push for Scottish independence.

After declaring he was a “Unionist to my finger-tips,” he was picked up on a remark he made last week when asked what came first, Brexit or the Union, he declared: "The Union, every time."

Yet when pressed that if there were a Brexit, possibly with no-deal, would he then be prepared to sacrifice the Union for that, Mr Hunt declared: “No…Of course, there are risks about what someone like Nicola Sturgeon would do politically if we had a no-deal situation and we would have to get through that. That is why a no-deal Brexit is not my first choice but, in the end, if the only way to leave the EU is without a deal, then I would do that.

“We would make a success of it and we will protect the Union but we would have to be very sensitive to the concerns that people like David Mundell raised because it would not be popular in Scotland.”

The Scottish Secretary has argued a no-deal Brexit would be “catastrophic” for the UK and Scotland and pose the biggest threat to the Union.

When it was suggested there was a fundamental contradiction in saying the Union would always come before Brexit while also stressing Britain would leave the EU without a deal if necessary, Mr Hunt told the BBC’s Andrew Marr Show: “No, because it is not a question of choosing one or the other.

“It’s a question of choosing a prime minister, who has the capability to deliver both. If you send to Brussels someone who can negotiate a deal, that can get through Parliament, then you won’t have a no-deal situation and then you reduce those risks.

“But I am also very clear we are going to leave the EU come what may and I will deliver that. If that happens, I will deliver it in a way that protects the Union because it’s absolutely vital we do.”

Meanwhile, Mr Johnson sought to underpin his own allegiance to the Union by announcing he would change the title of the PM’s office to include the phrase “Minister for the Union”.

The frontrunner to succeed Theresa May also said he would set up a new unit in No 10 to “sense-test and stress-test every policy for results it may bring to Union”.

Elsewhere, the PM appeared to launch a thinly-veiled attack on Mr Johnson’s “do or die” approach to Brexit. Attending her last European Council, she said: “I’ve always been very clear the best approach for the UK is to first of all ensure we’re delivering on the vote that took place in 2016, leaving the EU, but that we do that with a good deal so we can do it in an orderly way.”