Rishi Sunak has pleaded with Tories not to view Boris Johnson's final months with "rose tinted glasses" as he brutally trashed his own party's record.
The PM wannabe said the government he served in "wasn't working as it should" in recent months, and said it found itself "on the wrong side of a serious ethical issue".
In an attack on his own party's record, he said his rival Liz Truss was "sticking with the failed orthodoxy of the last 10 years" with her tax plans. The Conservatives have been in power since 2010.
Mr Sunak is scrambling to make up ground in the race for No10, with ballots due to start arriving on Tory members' doorsteps from today.
The ex-Chancellor secured the most support among Conservative MPs in the first round of the contest but polls have put Ms Truss ahead among Tory members.
Mr Sunak has tried to outgun his rival by pledging a 4p cut in Income Tax for nearly 30million Brits - but only by the end of the decade.
He denied that the vow was a panic move after being accused of "jam tomorrow" by Ms Truss' allies.
"I think it's right that people know where I want to take the economy," he told BBC Radio 4's Today programme.
"But it's entirely different to doing things right now that would make the situation far worse and endanger people's mortgages which is not something I want to do."
He urged Tory members not to look back at Boris Johnson's final months in power with "rose tinted glasses" amid a grassroots push to get Mr Johnson on the ballot paper.
Asked if he was a "backstabber", Mr Sunak said: "I do think there’s a risk that people are looking at the last few months of Government with slightly rose tinted glasses about what it was really like, because it wasn’t working as it should and crucially the Government found itself on the wrong side of a very serious ethical issue.
“And for me, also, going down the wrong economic path.”
Mr Sunak quit as Chancellor as Mr Johnson's handling of allegations of groping against Tory whip Chris Pincher appeared to be the final straw for Tory MPs.
Despite being Cabinet for more than two years, he said he was not a victim of "Treasury orthodoxy" and argued he'd ripped up the rules to come up with the furlough scheme.
And he accused Ms Truss of pursuing the "failed orthodoxy" of low corporation taxes.
He said: "What she's suggesting is entirely sticking with the failed orthodoxy of the last 10 years. I want to do something radical and different to get this economy growing."
It comes as Chancellor Nadhim Zahawi threw his weight behind Ms Truss and took a swipe at "doomster" Sunak.
He wrote in The Daily Telegraph: "Liz understands that the status quo isn't an option in times of crisis...
"We need a 'booster' attitude to the economy, not a 'doomster' one, in order to address cost-of-living woes and the challenges on the world stage.
"Liz will overturn the stale economic orthodoxy and run our economy in a Conservative way."
But Mr Sunak received a boost with the endorsement of Damian Green, the chair of the One Nation group of Conservative MPs, who said he could "unify the party" and "conjure up a solution" to crises.
