Rishi Sunak has defied calls to sack Sir Gavin Williamson despite conceding the senior minister’s threatening and abusive texts to a colleague are “not acceptable”.

The Prime Minister is under fire for bringing Sir Gavin back into the Government when he knew he was under investigation for allegedly bullying former chief whip Wendy Morton.

Downing Street said Sir Gavin maintains the full confidence of Mr Sunak, who insisted he would not act against the Cabinet Office minister until the outcome of a Tory party investigation.

Labour leader Sir Keir Starmer argued that the twice-sacked minister is “clearly not suitable” for the job and that Mr Sunak appointing his ally to Government shows he is “weak”.

In a series of expletive-laden texts exposed over the weekend, Sir Gavin accused Ms Morton of seeking to “punish” MPs out of favour with then-premier Liz Truss by excluding them from the Queen’s funeral, warning: “There is a price for everything.”

Mr Sunak told broadcasters travelling with him to the Cop27 climate summit in Egypt that he would not be “passing judgment” until after an “independent complaints investigation”, understood to be the internal investigation launched by the Tory party.

“I want to see the results of that, obviously, but I’ve been very clear that language is not right, it’s not acceptable,” he said.

“And that’s why I welcome the fact that Gavin Williamson has expressed regret about that and now wait to see what the investigation says.

“There’s an independent complaints process that’s being conducted at the moment. It would be right to let that process conclude before making any decisions about the future.”

Former Conservative Party chairman Sir Jake Berry said he informed Mr Sunak on the day he took the reins as Tory leader that Ms Morton had lodged a formal complaint over the messages.

But the PM went ahead with the appointment anyway the next day, with Downing Street citing his belief that Sir Gavin would make an “important contribution” to Government.

Mr Sunak has insisted he was unaware of the details of the exchange at the time he brought Sir Gavin back into Government, in the vague role of “minister without portfolio”.

Asked on Monday if the Prime Minister had full confidence in the Cabinet Office minister, his official spokesman said: “Yes.”

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Pressed on why Mr Sunak gave Sir Gavin the job, he added: “Obviously he thinks he has an important contribution to make to Government.”

Sir Keir told broadcasters that it was “disappointing” to be having a discussion about the Prime Minister’s judgment “yet again”.

“He’s clearly got people around the Cabinet table who are not fit to be there,” he said during a visit to Imperial College London.

“That is because he was so weak and wanted to avoid an election within his own party.”

Lib Dem chief whip Wendy Chamberlain said the Cabinet Office minister should be fired, as “in any other workplace, someone who behaved as he did would have been rightly dismissed for gross misconduct”.

“Every day Williamson remains in his post is an insult to the decent hardworking people across the country,” she said.

But Sunak ally and former Cabinet minister George Eustice played down the row as “a storm in a teacup”, questioning why a complaint had been raised in the first place.

“It was wrong, (Sir Gavin) shouldn’t have used that sort of language, he shouldn’t have adopted that sort of tone. It’s a minor storm in a teacup in the scheme of things with all the other great challenges that we face,” he told Times Radio.

“He was very frustrated and personally I’m not quite sure why the chief whip sort of referred this up to the … Conservative Party, rather than just try and resolve it between the two of them.”

Gavin Williamson abusive texts allegations
Cabinet Office Minister Sir Gavin Williamson is under investigation for alleged bullying (Victoria Jones/PA)

The Prime Minister’s spokesman said Mr Sunak has a zero-tolerance approach to bullying inside Government but would not commit to a timeline for appointing a new ethics adviser.

“There is a process ongoing. We’ll update you as soon as possible,” he said.

In the messages, obtained by The Sunday Times, Sir Gavin complained it was “very poor” that MPs who were not “favoured” had been excluded from the Queen’s funeral at Westminster Abbey.

Ms Morton repeatedly insisted that his claims were unfounded and that the Government had been allocated an “extremely limited” number of tickets.

Sir Gavin responded: “Well certainly looks it which I think is very shit and perception becomes reality. Also don’t forget I know how this works so don’t puss (sic) me about.

“It’s very clear how you are going to treat a number of us which is very stupid and you are showing f*** all interest in pulling things together.

“Also this shows exactly how you have rigged it is is (sic) disgusting you are using her death to punish people who are just supportive, absolutely disgusting.

“Well let’s see how many more times you f*** us all over. There is a price for everything.”

Sir Jake told the paper that he was informed by the Conservative Party chief executive on October 24 – the day before Mr Sunak formally took office – that a formal complaint had been made against Sir Gavin.

“In compliance with protocol, in my capacity as party chairman, I informed both the new Prime Minister and his incoming chief of staff about the complaint on the same day,” he said.

Sir Gavin, who was knighted by Boris Johnson earlier this year, is a divisive figure at Westminster where he is viewed with suspicion by many Tory MPs because of his reputation as an inveterate plotter.

He was sacked first by Theresa May as defence secretary for leaking details of a National Security Council meeting and then by Mr Johnson as education secretary over the Covid-19 A-levels debacle.

However, he was regarded as a key figure in Mr Sunak’s campaign over the summer to become party leader.