Rishi Sunak says it is “right” for an independent complaints investigation to take place into accusations of bullying made again Sir Gavin Williamson “before making any decisions about the future”.

Sir Gavin, the cabinet minister and former education secretary, allegedly sent abusive text messages to Wendy Morton, the former chief whip, complaining that he and other colleagues had been excluded from the Queen’s funeral for political reasons.

Speaking from COP27 in Egypt, Mr Sunak, the prime minister, said he had been “very clear that the language is not right [and] not acceptable”, adding: “That’s why I welcome the fact Gavin Williamson has expressed regret about that.”

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Pushed on why he was keeping Sir Gavin in his top team despite condemning his actions, Mr Sunak reiterated the party was carrying out an independent investigation.

Earlier, the prime minister’s official spokesman said Mr Sunak welcomed that Sir Gavin “expressed regret” about the messages sent to his colleague, and that he had a zero tolerance approach to bullying inside government.

Asked if Mr Sunak has full confidence in former defence secretary Sir Gavin, the spokesman replied: “Yes.”

He added that Mr Sunak believes Sir Gavin has an “important contribution” to make to government.

Mr Sunak is under pressure over bringing Sir Gavin back into the government.

The spokesman said at the time that Mr Sunak “knew there was a disagreement”, but was not aware of the “substance” of the messages.

‘Heat of the moment’

Clarifying this on Sunday, Oliver Dowden, the chancellor of the duchy of Lancaster, told Sky News’ Sophy Ridge on Sunday programme that Mr Sunak knew there was a “difficult relationship” between Sir Gavin and Ms Morton, but “wasn’t aware” of “specific allegations” until Saturday evening.

Mr Dowden added that Sir Gavin “regrets the language he used” and also suggested that a number of individuals had “a difficult relationship” with Ms Morton.

“These were sent in the heat of the moment expressing frustration. It was a difficult time for the party. He now accepts that he shouldn’t have done it and he regrets doing so. Thankfully, we are in a better place now as a party,” he said.

Labour has called for an “urgent independent investigation” into the appointment of Sir Gavin, with shadow climate secretary Ed Miliband warning against a “cover-up” over the allegations.

Speaking to Sophy Ridge, Mr Miliband said the matter “really calls into question Rishi Sunak’s judgement and the way he made decisions about his cabinet”, adding Sir Gavin’s reappointment was “not in the public interest”.

“There needs to be an urgent independent investigation into exactly what happened. We can’t have a cover-up, we can’t have a whitewash here,” he said.

“What did Rishi Sunak know? When did he know it? What did Gavin Williamson do and what are the implications of that?”

‘Not suitable for job’

Labour leader Sir Keir Starmer said Sir Gavin is “clearly not suitable” for the job, calling his appointment a sign of how “weak” Mr Sunak is.

“I think that the prime minister has got people who are clearly not fit for the job around the cabinet table,” he said.

Screenshots leaked to The Sunday Times appear to show expletive-laden messages from the South Staffordshire MP, including a warning that “there is a price for everything”.

Another message reads “think very poor how [privy councillors] who aren’t favoured have been excluded from the funeral”.

A source confirmed to Sky News that the contents of the messages were accurate.

Sir Jake Berry, the former chairman of the Conservative Party, has said he told Mr Sunak a bullying complaint had been made against Sir Gavin a day before he entered Number 10.

Sir Gavin has been approached for comment.

The Sunday Times quoted the Cabinet Office minister as saying: “I of course regret getting frustrated about the way colleagues and I felt we were being treated. I am happy to speak with Wendy and I hope to work positively with her in the future as I have in the past.”

Liberal Democrat deputy leader Daisy Cooper accused Mr Sunak of ignoring the complaint and called for Sir Gavin to be sacked.

George Eustice, the Tory former environment secretary, described the matter as “a storm in a teacup”.

“I think Gavin’s apologised for this, he accepts it’s wrong to use that kind of language but equally he was very frustrated and I’m not quite sure why the chief whip referred this up the party instead of trying to resolve it between the two of them,” he told Sky News.

Mr Eustice continued: “It was wrong, he shouldn’t have used that sort of language – and the chief whip probably should have been talking to him instead of texting him – but it is a storm in a teacup in the context of the great challenges we face”.

At the weekend, a Tory party spokesman said: “The Conservative Party has a robust complaints process in place. This process is rightly a confidential one, so that complainants can come forward in confidence.”

Sir Gavin was sacked as defence secretary in 2019 after the leaking of confidential information from the National Security Council.

After being appointed education secretary by Boris Johnson, he was dismissed from cabinet again in 2021 after controversy around the grading of exams during the pandemic.

It marks the second major controversy to erupt over Mr Sunak’s cabinet appointments, with the prime minister already under fire for making Suella Braverman his home secretary days after she was sacked for security breaches.