The First Minister’s plans for breaking away from the UK were rubber-stamped by SNP members at their conference last weekend, with a majority for the party being set as the bar for another referendum, as it was in 2011.

But the Prime Minister questioned why, after 18 years in power, the First Minister is not seeking to focus on his party’s record in Government ahead of next year’s election.

John Swinney told the PA news agency earlier this month that if he was to win the majority he seeks in May, the Prime Minister would likely resign.

Asked about the comments as he spoke to Scottish journalists in Downing Street on Monday, Sir Keir Starmer said: “He’s insulting the intelligence of the Scottish people.

“After 18 years in Government he really needs to explain to you why he’s not running on his record.”

At the general election in 2029, the Prime Minister added, Labour will be running on its record in Government.

“I’m going to go to the country on the basis of what we’ve done for the country,” he said.

“You have to ask him why he doesn’t want to run the election on his record.

“Essentially, there’s a blindingly obvious reason for that, and that’s it’s an appalling record.”

SNP depute leader Keith Brown said: “Keir Starmer’s reverse Midas touch even extends to his own political attacks, he points to waiting lists and police numbers, when waiting lists are falling in Scotland and rising in England, and Scotland has more police officers per head than Labour-run England and Wales.

“He even talks about Great British Energy, which has so far created 13 jobs in Aberdeen, compared to the 1,000 which were promised.

“This is a Prime Minister who just cannot get anything right. Once again, Keir Starmer is showing just how little he knows about Scotland.

“The abject failure of Keir Starmer’s Labour Government shows that the Westminster system will simply never work for Scotland and we need the fresh start of independence.”