The Prime Minister retains full confidence in Sir Gavin Williamson despite the emergence of threatening and abusive texts sent by the senior minister to a female colleague.

Rishi Sunak 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.

Labour leader Sir Keir Starmer has said the Cabinet Office minister is “clearly not suitable” for the job and claimed Mr Sunak was “weak” to appoint him.

But he still has the Prime Minister’s backing, according to No 10, while Mr Sunak maintains a zero-tolerance approach to bullying within Government.

In a series of texts exposed over the weekend, Sir Gavin angrily accused Ms Morton of seeking to “punish” MPs like him who were out of favour with then-premier Liz Truss by excluding them from the Queen’s funeral.

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.

The Prime Minister has said the texts were not “not acceptable or right”, while Cabinet minister Grant Shapps earlier echoed this sentiment – describing the correspondence as “completely inappropriate”.

But with questions raised over his judgment, Mr Sunak has sought to clarify what he knew and when.

While he was aware of a “disagreement”, he has said he was not party to the details of the exchange at the time he brought Sir Gavin back into Government.

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 during a visit to Imperial College London 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.

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

He reiterated Labour’s calls for a general election, arguing that the public deserve a vote as debates persist over the “weak position the Prime Minister is in”.

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.”

The Prime Minister’s spokesman said he was “not aware” whether Mr Sunak had spoken with either Sir Gavin or Ms Morton since the matter came to light but stressed he would not normally get into details of private conversations.

He said Mr Sunak has a zero-tolerance approach to bullying inside Government.

However, he 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 weren’t “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 retorted: “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.