BORIS Johnson’s remarks have infuriated his old Better Together allies, who’ve accused him of being a bigger threat to the Union than Nicola Sturgeon.

Alistair Carmichael, the former secretary of state for Scotland and a key figure in the first independence referendum’s No campaign, said the Prime Minister’s “mask has slipped”.

He said under Ruth Davidson’s leadership the Tories tried to move on from their previous anti-devolution stance, but Johnson’s comments had, he said, blown that “sky high”.

Carmichael added: “We’ve got a massive mismatch between what Boris Johnson says in public and what he says in private. And you know, for the man who took to himself the title of Minister for the Union when he became Prime Minister you have to think with friends like this who really needs enemies.

“Boris Johnson now is a bigger threat to the continuation of the United Kingdom than Nicola Sturgeon or Alex Salmond could ever hope to be.”

Asked if he bought Robert Jenrick’s insistence that Johnson hadn’t meant devolution in general but what had been done with it, Carmichael said: “There can be no conditions attached to your support for devolution – you’re either in support of it or you’re not.

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“As Minister for the Union, if Boris Johnson cannot accept that devolution is the settled will of the Scottish people, then seriously he should not be in that job.”

The presenter then asked Carmichael if the “disaster” comment made Scottish independence more likely.

He replied: “Boris Johnson is not making it easier to resist another referendum. But in essence the arguments do not change.”

Labour’s Ian Murray agreed: “Well it’s that bombastic approach, that buffoonery, that always has bestowed Boris Johnson. He is a tremendous threat to the Union.”

He said Johnson had to “take half a step back here, as the current incumbent in Downing Street and the custodian of the United Kingdom and realise that his Government are doing everything possible to become that United Kingdom.”

Scottish Labour leader Richard Leonard said the remarks exposed “the underlying thinking and philosophy in Downing Street”.

He told BBC News the comments were “reminiscent of the voices of Thatcherism and Majorism of the 1980s and 1990s, which were steadfastly opposed to devolution”.

“In my view, what Boris Johnson is doing is defying the popular will of the people of Scotland, and I don’t think that’s a very good place for any prime minister to be in.”

Scottish Greens co-leader Patrick Harvie said voters shouldn’t be surprised by the comments.

He said: “Boris Johnson has called Scotland’s public health achievements, free prescriptions and university tuition and Scottish Green achievements like free bus travel for young people, fairer taxes and equal protection for children a ‘disaster’.

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“We shouldn’t be surprised. The Tories campaigned against the creation of the Scottish Parliament in the first place and are now seeking to overrule it with their illegal Internal Market Bill. This attack on our democracy cannot win, and will only wake more people up to the fact that Scotland can play a leading role in Europe without Westminster holding us back.”

The remarks were also raised in the Senedd where Welsh First Minister Mark Drakeford said they betrayed an “old hostility” on the part of the Tories towards devolution.

He said: “Devolution thrives when there is a Labour government to support it, and devolution comes under the sorts of pressures that it is now under when we have a Conservative government – when you scratch the surface of the Conservative Party and all its old hostility to devolution rises back to the surface.

“That’s what happened yesterday when the Prime Minister thought he could show off in front of a few Conservative MPs from the north of England.”