BORIS Johnson has been urged to explain how much taxpayers’ money is been spent on his Union Unit after two key advisers quit in a fortnight.

Oliver Lewis, a veteran of the Vote Leave Brexit campaign, left on Friday and is reported to have said his position was made “untenable” by others within Number 10.

He had replaced former Scottish MP Luke Graham as head of the unit earlier in February, who lasted less than a year in the job.

SNP MP Stewart Hosie said taxpayers have a right to know how much public money the Prime Minister has spent on his anti-independence campaign.

He said spending was “spiralling out of control”, including salaries of £110,000-£114,999 for Lewis and £90,000-£94,999 for Graham.

READ MORE: Nicola Sturgeon hits out at Union Unit for saying knowledge of Scotland isn't needed

Hosie said another example was an estimated £1-£2 million for an additional 30 to 50 officials that Downing Street sources told the media would be hired.

He said: “The Tories are in turmoil and their anti-independence campaign is in tatters. Boris Johnson must come clean over how much taxpayers’ money he has wasted on this shambles.

“This is the latest example of Tory cronyism, with jobs for the boys being handed out like sweeties.

“Spending on Tory advisers is spiralling out of control, while the public foots the bill for their six figure salaries. Taxpayers have a right to know how much money is being spent.”

He added: “Twenty-one consecutive polls have shown a majority for independence. Despite what the Tories claim in public, there is no doubt they are gearing up for a post-pandemic referendum.”

Yesterday it was claimed Lewis had quit after being accused of briefing against Michael Gove, with one source saying it was a “complete clear out” of anyone associated with departed former Number 10 adviser Dominic Cummings.