BORIS Johnson has blamed the SNP’s “campaign to destroy the union” as the reason for his plummeting popularity in Scotland.

A recent YouGov poll suggested 65% of Scottish voters believing he will be a “poor” or “terrible” Prime Minister, while 69% think him incompetent, and 71% consider him untrustworthy. The Prime Minister defended his appeal as he spoke to journalists in Faslane.

He also refused to rule out banning a second independence referendum during his visit to Scotland on Monday, but said he saw “no reason” to have another vote - though he appeared to be unsure how many indyrefs there have been.

He also lavished praise on Ruth Davidson, insisting he would work to help her become the next First Minister.

The two have a frosty relationship which has become positively glacial in recent days, in part because Johnson ignored Davdison’s pleas to keep David Mundell in post as Secretary of State for Scotland, and in part because of Davidson’s refusal to back Johnson’s no-deal Brexit.

Talking to journalists during his visit to Faslane, the Prime Minister was asked if there were any circumstances under which he would allow a second independence referendum, Johnson replied: “This is formulated in the wrong way, if I may say. Because what has happened, is in 2014 there was a historic vote.

“It was – I think it was the only one that’s been in my lifetime, that I can remember.

“Yes? I think it was. The only vote Scottish independence that I can remember, in my lifetime, and I’m 55.

“It’s the only time it’s happened, and it was decisive. There was I think at least a 10-point margin and everybody made clear at the time in 2014 - even the Scottish nationalists party, I seem to recollect – said that this was a once in a generation vote.

“And I think that the confidence of the public in politicians will be undermined yet further and hold another referendum. It was clear, it was decisive. The union is fantastic - it’s the most successful political partnership anywhere in the world, so let’s keep it going.”

Asked if he was ruling out, he replied: “It was a once in a generation consultation of the people. We did it in 2014 and the people were assured then that it was a once in a generation consultation.

“I see no reason now for the politicians to go back on that promise.

“As I’ve said I think it would be wrong to go back on the promise to the people of the United Kingdom but above all to the people of Scotland – that when they went out to the polls in 2014 it was a once in a generation consultation. They voted decisively.”

Johnson also blamed the SNP’s “campaign to destroy the union” as the reason for his unpopularity in Scotland.

“I think that my ambitions to take the UK out of the EU whole and entire and perfect. Clearly they contradict the ambitions of the SNP and I think that their policies are entirely nonsensical.”

Asked about Davidson, the Prime Minister replied: "I'm a number one fan of Ruth Davidson and what she's done for Scottish Conservatives.

"It's she who is taking the fight to the Scottish nationalists, those who would destroy the union.

"She's been fantastically successful and I admire her brand of Conservatism very much.

"Indeed, she and I share a huge range of political beliefs and our core philosophy is the same."