Whitehall's anti-corruption panel said the former prime minister - who has vowed to offer uncensored views - had not sought its advice on the matter within an appropriate timeframe.

Former ministers are meant to apply to the Advisory Committee on Business Appointments (Acoba) before taking up a new appointment or role for up to two years after leaving government.

An Acoba spokesperson said: "The Ministerial Code states that ministers must ensure that no new appointments are announced, or taken up, before the committee has been able to provide its advice.

"An application received 30 mins before an appointment is announced is a clear breach.

"We have written to Mr Johnson for an explanation and will publish correspondence in due course, in line with our policy of transparency."

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Earlier, a source close to Mr Johnson insisted that he had written to Acoba, but did not say when the letter was sent.

The Daily Mail, a right-leaning outlet and one of Mr Johnson's biggest supporters, confirmed on Friday that it had hired Mr Johnson as a weekly columnist, calling him "one of the wittiest and most original writers in the business".

In a video shared alongside the announcement, Mr Johnson said he was "thrilled" to contribute to "those illustrious pages", and promised to deliver "completely unexpurgated stuff".

Although he quipped he will only cover politics when "I absolutely have to", the column gives him a powerful platform to take shots at Prime Minister Rishi Sunak with whom he has been publicly clashing.

But the announcement, which comes a day after the privileges committee concluded Mr Johnson lied to parliament with his denials of Downing Street lockdown parties, has drawn the ire of opposition MPs.

Labour MP Angela Eagle said "this is what no shame looks like".

Former shadow chancellor John McDonell said he could not think "of a more appropriate vehicle for Johnson to peddle more of his lies" than in the newspaper, which he claimed was a "rag" that "contributes so much to dividing our society and lowering the standards of public life".

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There has been speculation about whether Mr Johnson would return to his journalism roots after he dramatically quit as an MP last week ahead of the damning privileges verdict becoming public.

Before he became party leader, Mr Johnson received a £275,000 salary to write for The Telegraph, which will likely pale in comparison to the sum he will pocket as a former premier.

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POLITICO, which first broke the news of Mr Johnson's new writing gig, reported he will receive a "very high six figure sum".

News of his lucrative new job came as the prime minister was urged to "stand up to" his predecessor and force him to pay back the tax payer cash spent on his partygate legal fees.

Mr Johnson joins the ranks of his staunch ally Nadine Dorries, who writes a weekly Tuesday column for the Daily Mail.

The former culture secretary, who has also announced her exit from the Commons, used her most recent piece to suggest "sinister forces" were behind the decision to exclude her from Mr Johnson's controversial resignation honours list - something Downing Street has denied.

The former long-standing Daily Mail editor Paul Dacre was also once tipped to be on the list but was reportedly removed during the House of Lords vetting process.