Boris Johnson broke ministerial rules when he signed up to write a column for the Daily Telegraph just days after quitting as foreign secretary, a watchdog has said.

The Advisory Committee on Business Appointments (Acoba) – which vets appointments by ex-ministers and senior officials – said it was "unacceptable" that he agreed a contract with the newspaper before contacting them.

It comes as Mr Johnson faces a disciplinary hearing by the Conservative party after saying Muslim women wearing face veils looked like “bank robbers” and “letter boxes”

Rules state that former ministers are required to consult Acoba before any new appointments are announced or taken up.

However, the committee said Mr Johnson only notified them of his Telegraph appointment on July 26, two weeks after he signed the contract and after the paper announced that he would be resuming the weekly column which he gave up when he became foreign secretary in 2016.

In a letter to Mr Johnson, published on the committee's website, Acoba chairwoman Baroness Browning said: "The committee considers it to be unacceptable that you signed a contract with The Telegraph and your appointment was announced before you had sought and obtained advice from the committee, as was incumbent on you on leaving office under the Government's business appointment rules.

"Failure to seek advice before The Telegraph made public you would be taking on this work and before signing a contract was a failure of your duty to seek advice."

She said that under the rules, there was a minimum three-month waiting period during which ex-ministers should not take up outside appointments after leaving office.

"The committee sees no reason why the minimum three month waiting period should not have been observed in this case and considers that your entering into this appointment within a few days of leaving office without seeking the advice of the committee was a breach of the rules," she said.

She noted the permanent secretary at the Foreign Office Sir Simon McDonald had written to Mr Johnson on the day he resigned reminding him of his obligations, but that Mr Johnson had told the committee he did not receive the letter until after he signed the contract.