Former Conservative Party chairman Sir Jake Berry informed Mr Sunak on the day he took office that the then chief whip Wendy Morton had lodged a formal complaint over a series of abusive and threatening texts.
Sir Gavin angrily accused her of seeking to “punish” MPs like him who were out of favour with Liz Truss by excluding them from the Queen’s funeral.
The exchange of messages concluded with him saying: “Well let’s see how many more times you f*** us all over. There is a price for everything.”
Despite the disclosure, Cabinet Office Minister Oliver Dowden insisted that the Prime Minister still had confidence in Sir Gavin, who is now also a minister in the Cabinet Office.
Mr Dowden confirmed the Prime Minister had been aware there had been a complaint made against Sir Gavin but said he had not known the details of the exchange.
Sir Gavin, who was knighted by Boris Johnson earlier this year, is a divisive figure at Westminster. 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.
A Conservative Party spokesman: “The Conservative Party has a robust complaints process in place.”
d the way he made decisions about his Cabinet.”
Mr Dowden said Sir Gavin regretted sending the messages to Ms Morton at what had been a “difficult time” for the Conservative Party following the election of Ms Truss as leader.
“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,” Mr Dowden said.
In the messages, Sir Gavin complained it was “very poor” that MPs who “aren’t favoured” had been excluded from the funeral of the Queen 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 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.