A Cabinet minister has denied that the Prime Minister considers devolution to have been “a disaster”, but stressed he was “very troubled” by Scottish nationalists’ attempts to split up the United Kingdom.

SNP leader Nicola Sturgeon seized on comments made by Boris Johnson after he told Conservative MPs that devolution had been “a disaster north of the border” and called it “Tony Blair’s biggest mistake”.

Downing Street sources did not deny Mr Johnson made the comments, which were first reported by the Sun, during a discussion with the Northern Research Group of backbenchers on Monday.

But Communities Secretary Robert Jenrick told Sky News that was “not what the Prime Minister was saying”.

“The Prime Minister has always supported devolution but he is at heart a unionist and he is very troubled by the rise of nationalism and separatism,” he said.

In a later interview on Tuesday, Mr Jenrick also had choice words for those pushing for another independence referendum for Scotland, following 2014’s No result.

He told BBC Breakfast: “I also think, frankly, that any politician who wanted to hold a referendum on a topic like this at this moment in time…is frankly, mad.

“We’re in the middle of a very serious health situation, a pandemic, and we’re also seeing massive disruption to people’s lives and livelihoods as a result of the economic disruption that’s flowed with it.”

Mr Johnson’s reported comments, which come just a few months before the Scottish Parliament elections next year, have caused fresh controversy over the union, with the comments being used by nationalists to back up their arguments for full autonomy.

In response to the remarks, which also included Mr Johnson saying he could not “see a case” for handing down more powers, Scotland’s First Minister suggested independence was the best answer for the devolved administration.

Ms Sturgeon tweeted: “Worth bookmarking these PM comments for the next time Tories say they’re not a threat to the powers of the Scottish Parliament – or, even more incredibly, that they support devolving more powers.

“The only way to protect and strengthen the Scottish Parliament is with independence.”

Douglas Ross, who leads the Conservatives in Scotland, insisted that “devolution has not been a disaster”.

But shadow Scottish secretary Ian Murray criticised Mr Johnson as he defended devolution as “one of Labour’s proudest achievements”.

“This confirms that Boris Johnson doesn’t believe in devolution and would put the future of the United Kingdom at risk,” the Labour MP said.

The row comes only a month after the UK’s three devolved administrations raised concerns over the Westminster Government’s UK Internal Market Bill, with the Scottish Government describing the legislation as a “power grab”.

Analysis of a study examining public opinion at the beginning of November also suggested the pursuit of Brexit is undermining support for Scotland remaining in the UK.