Boris Johnson has accused Rishi Sunak of "talking rubbish" amid a bitter row between the pair over peerages and gongs to the ex-PM's close allies.
The statement came just hours after the PM hit back at his predecessor, saying he had asked him "to do something that I wasn't prepared to do" over Lord's appointments.
Mr Sunak said the former Tory leader had asked him to overrule the vetting committee for appointments to the House of Lords "or to make promises to people".
He added: "Now, I wasn't prepared to do that because I didn't think it was right and if people don't like that then tough".
But Mr Johnson said: "Rishi Sunak is talking rubbish.
"To honour these peerages it was not necessary to overrule Holac - but simply to ask them to renew their vetting, which was a mere formality."
The extraordinary public outburst came after days of bitter Tory in-fighting since the publication of Mr Johnson's resignation honours list.
The former Prime Minister’s allies have accused Mr Sunak of interfering in Mr Johnson’s resignation honours list - and denying accolades for Nadine Dorries and Sir Alok Sharma.
No10 has denied the claims and on Monday said there are no plans to change the "long-standing convention" of resignation honours list.
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"I think it's for former prime ministers to explain their rationale for nominating individuals," the Prime Minister's official spokesman said.
But he added that a resignation honours list was a "long-standing convention".
It also emerged on Monday the former PM, who announced he was quitting as an MP last week, had written to the Chancellor to formally resign from the Commons.
Shortly afterwards, it was officially announced the ex-PM is no longer an MP, as he was given an arcane title to allow him to stand down.
In a statement the Treasury said: "The Chancellor of the Exchequer has this day appointed Alexander Boris de Pfeffel Johnson to be Steward and Bailiff of the Three Hundreds of Chiltern."
