Allegations were made against the former education secretary - who had also served as a chief whip - back in November last year after Sir Gavin sent a number of text messages to her, including one that warned her "there is a price for everything".

It led to him resigning as a Cabinet Office minister from Rishi Sunak's newly formed government, with a pledge to "clear my name of any wrongdoing".

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The accusations surfaced in the media two weeks after Mr Sunak took the keys to Number 10 after the political downfall of his short-lived predecessor Liz Truss.

Ms Morton, who had served under her as chief whip, told parliament's Independent Complaints and Grievance Scheme (ICGS) that Sir Gavin had sent her a series of text messages in September after he was not invited to the Queen's funeral, attributing the perceived snub as being down to him not supporting Ms Truss in the party's leadership election.

She claimed the messages were "threatening", "intimidating" and "undermining".

At the time, Mr Sunak said he had full confidence in Sir Gavin, though he welcomed the ICGS's investigation into the case.

The IGCS investigator concluded Sir Gavin was in breach of bullying and harassment policy. However, the decision was overturned by the Standards Commissioner Daniel Greenberg, leading Ms Morton to appeal.

The Independent Expert Panel (IEP), which handles such cases, today released its own report, upholding her complaint.

It showed phrases from the message from Sir Gavin, including:

• "Don't forget I know how this works so don't [push] me about"

• "It's very clear how you are going to treat a number of us which is very stupid and you are showing **** all interest in pulling things together. Don't bother asking anything from me"

• "Well let's see how many more times you **** us all over. There is a price for everything"

• "You are using her death to punish people who are just supportive, absolutely disgusting"

The IEP ruled Sir Gavin should make a personal statement to the House apologising for his actions, as well as undergo training "to avoid a repetition of similar behaviour and increase his awareness of the impact of bullying on others".

They described the messages as "an abuse of power" and said his conduct had "gone beyond vigorous complaint or political disagreement to a threat to lever his power and authority as a former chief whip to undermine her personally as revenge".

The IEP said it had "considered carefully" whether he should face suspension from the Commons, but had instead decided a "full and unreserved apology", along with behaviour training, was required.

The panel also said Sir Gavin had accepted the ruling.

Sir Gavin was recommended for a knighthood by Boris Johnson in 2022.

Despite holding a number of roles in government, he is also a controversial figure, having been sacked by Theresa May in 2019 for leaking details of a National Security Council meeting, and again by Mr Johnson as education secretary over the issues with A-levels during COVID.