FORMER prime minister Boris Johnson reportedly warned Dominic Raab about his conduct when the latter held several Cabinet positions during Johnson’s leadership.

The ex-Conservative lawyer is understood to have provided evidence to Adam Tolley KC, the independent lawyer looking into a number of formal complaints made by senior civil servants against Raab.

According to The Daily Telegraph, who first revealed Johnson had become involved in the bullying investigation into his former Cabinet colleague, it is “highly unusual” for a former prime minister to be involved in an investigation launched by Downing Street.

Both Johnson and Raab’s spokesmen have declined to comment to The Telegraph, The Times and the BBC on the matter.

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It has been one week since Raab, who has repeatedly denied the allegations against him, was interviewed by Tolley, indicating the official inquiry could be drawing to a conclusion.

Multiple sources with knowledge of the investigation told the PA news agency that the Deputy Prime Minister had been questioned by the senior lawyer.

It was unclear how many times he had been interviewed or when.

Raab has insisted he had “behaved professionally throughout” but said he would resign if an allegation of bullying was upheld.

During the investigation, Tolley would be expected to put the allegations to Raab before finalising his report.

Rishi Sunak has already resisted calls to suspend his deputy while under investigation, including from Tory party chairman Sir Jake Berry, Labour and the FDA union which represents senior civil servants.

Should the investigation be damning, Sunak will again face questions about what he knew about the allegations before brining Raab back into the Cabinet.

Downing Street has only ruled out the Prime Minister being aware of “formal complaints” although sources have previously said he had been warned about his ally’s behaviour.

The eight formal complaints centre on Raab’s tenures as foreign secretary, Brexit secretary and during his first stint as justice secretary.

Raab ordered the investigation into himself in November after coming under pressure following numerous claims, including that he was so demeaning to junior colleagues that many were “scared” to enter his office.