Rishi Sunak has been told to launch an investigation after a claim the Tory Party received a formal complaint of alleged "threatening" behaviour by Gavin Williamson, which he is said to deny.
Sir Gavin, who was sacked from both Boris Johnson and Theresa May's cabinets, was brought back into Government when Mr Sunak entered No10 last week.
But according to Tortoise a complaint has been submitted regarding Mr Williamson's conduct to Tory headquarters.
Wendy Morton, a former chief whip, has reportedly passed on details of "vile and threatening messages" she received in the dying days of Liz Truss's Government.
A Tory spokesman did not comment on the allegation, but told The Mirror: "The Conservative Party has a robust complaints process in place".
A friend of the Tory minister told Tortoise he "strongly refutes these allegations" and is "very happy to share all communications with the former chief whip with CCHQ if needed".
Sir Gavin played a key role in Mr Sunak's leadership campaign and was previously sacked as Defence Secretary by former PM Theresa May in 2019 after an inquiry regarding a leak from the National Security Council.
He then served as Education Secretary under Boris Johnson but was sacked in the September 2021 reshuffle.
After being crowned Tory leader and Prime Minister last week, Rishi Sunak appointed Sir Gavin as a Minister of State at the Cabinet Office.
Labour's Deputy Leader Angela Rayner said the reports raised "fresh questions about Rishi Sunak's woeful judgement in resurrecting ministers who left the Government under a cloud of misconduct".
Mr Sunak has in recent days also faced criticism over the reappointment of Suella Braverman as Home Secretary - six days after she resigned from Liz Truss's Government for breaching the ministerial code.
Ms Rayner demanded: "Given his [Sir Gavin's] new role and the seriousness of these allegations, there must be an urgent and independent investigation.
"Far from restoring integrity, professionalism, and accountability, Rishi Sunak is failing to stop the rot.
"He promised that appointing an independent ethics adviser would be one of the first things he would do as Prime Minister, but instead he has given us more of the same old sleaze."
The Mirror has contacted Sir Gavin for comment.
