Boris Johnson declared he was "epileptically bored" with Covid during an "almighty row" about free testing, a former aide has claimed.
The former PM - who quit last summer following a string of scandals - is claimed to have flown into a rage with Sajid Javid when he "dug in" over lateral flow tests.
And on another occasion Mr Johnson exploded "f*** this s***" and suggested clearing out the Treasury as tensions with Rishi Sunak built up, it is alleged.
The claims were made by Guto Harri, Mr Johnson's former communications chief, who said the relationship between the then-PM and his Chancellor became "untenable".
It is the latest revelation from Mr Harri, who previously said the ex-PM wanted to send Mr Sunak a message calling him a c*** as his leadership disintegrated.
Speaking on his Unprecedented podcast, Mr Harri said things came to a head with Mr Javid last year, when the PM refused to keep shelling out for Covid testing.
He said: ‘There was an almighty row over ending free universal Covid testing.
"The Saj dug in with a curiously well-rehearsed line about being asked to 'disarm when the enemy is still lurking out there'.
"But testing was costing £2 billion a month, dwarfing the budgets of entire departments. Boris, at the time, declared himself 'epileptically bored with Covid. What people are getting now is not killing them', he thought.
"'It's a matter of stupendous irrelevance, as long as we have a good pair of eyes in the crow's nest, so we will not miss another iceberg.'"
He claimed that Mr Johnson warned the Cabinet to stop talking about an upcoming recession, and said the PM got irritated by a "lack of oomph" in the Treasury.
Mr Harri said: "And I think that's when the tension between him and the then Chancellor, Rishi Sunak, who's now Prime Minister, of course, started to ramp up until it got to the point where it was basically untenable. "
"'If Rishi is a Thatcherite, let's have it' he moaned on one occasion without any expectation, sadly, that he'd ever oblige.
"And on another time, he just blew up, 'f*** this s***"' he said. 'We need to clear out the Treasury. Begin a new as Singapore-on-Thames. The department has basically become a bank manager. The computer just says no.'"
Mr Johnson complained the Chancellor wrote "too many cheques but got very little value for money", Mr Harri said, and added that he doubts Mr Sunak would have lasted the summer without being sacked.
"It was time for tax cuts, deregulation, and dynamism," Mr Harri said.
"Then there was this rare moment of open defiance from the Chancellor, who reminded the Prime Minister, that it had been his vision to spend vast amounts of taxpayer funds on endless infrastructure projects, on new hospitals, on extra cops, extra doctors, extra nurses, extra all kinds of things.
"And he used a very memorable phrase, "We had a song for a long time. Do we not want to sing it anymore?"
Listen to the fourth episode of Unprecedented on Global Player .
