An inquiry into Sue Gray’s proposed move to the Labour Party has been put on hold after the partygate investigator refused to take part in the probe, a government minister has said.

Her appointment as the Labour leader’s chief-of-staff proved hugely controversial among Tory MPs given that she led the official government probe into Downing Street rule-breaking during lockdown.

Some reports suggested she could have breached the civil service code with her job move.

According to an update on a review into the appointment, Gray declined to make representations into the inquiry looking into her discussions with Labour about the senior party role, Oliver Dowden has said.

In a written statement to the House of Commons on Tuesday, cabinet office secretary Oliver Dowden said his department has made a “confidential assessment” to the anti-corruption watchdog and will not provide further information on Gray’s departure “whilst we consider next steps”.

As well as a cabinet office probe, the anti-corruption watchdog, the Advisory Committee on Business Appointments (Acoba), is reviewing the terms of Gray’s departure.

It can set recommendations for when senior people leave government, including calling for a cooling-off period to avoid any conflict of interest.

Who Is Sue Gray?

The senior civil servant was thrust into the limelight when she took over the probe into coronavirus rule-breaking at No 10 in 2021.

She stepped in to lead the investigation after cabinet secretary Simon Case – her boss – recused himself following allegations that his own office held a Christmas event amid a lockdown.

An initial dossier, published in January 2022, included several strong criticisms of Downing Street’s drinking culture, but was short on details about the parties as it was hampered by an investigation launched by the Metropolitan Police.

But her full report in May 2022 proved to be a bombshell. It detailed events at which officials drank so much they were sick, sang karaoke, became involved in altercations and abused security and cleaning staff at a time when millions of people across the country were unable to see friends and family.

She criticised “failures of leadership and judgment” in No 10 and said “the senior leadership at the centre, both political and official, must bear responsibility”.

Six weeks later, Johnson was forced out of office by his own cabinet and Conservative MPs.

While Gray, in her mid-60s, is said to shun the media spotlight, some politicians have gone so far as to suggest the former publican is the “real leader” of the UK.

In her former role as director-general of propriety and ethics in the Cabinet Office from 2012 to 2018, she is said to have overseen cabinet reshuffles, served as a guiding hand in compiling honours lists, and even signed off political memoirs before their publication.

In the statement, Dowden said Gray was “given the opportunity to make representations as part of this process but chose not to do so”.

He added that “in order to maintain confidentiality towards an individual former employee, I am unable at this stage to provide further information relating to the departure of Ms Gray whilst we consider next steps”.

Dowden also highlighted sections of the civil service code relating to the political activity of civil servants, adding: “The impartiality and perceived impartiality of the Civil Service is constitutionally vital to the conduct of government.”

Earlier in the day Starmer insisted he had no discussions with Gray while she was investigating Boris Johnson and he was “confident” she had not broken any rules.

“Firstly I had no discussions with her while she was investigating Boris Johnson whatsoever, I don’t think anyone is suggesting that’s the case,” the Labour leader told BBC Breakfast ahead of an expected update later from the Cabinet Office on the circumstances of her departure.

He went on: “I’m confident she hasn’t broken any of the rules.”

Starmer claimed the government was trying to resurrect a story about Gray, because they do not want to talk about the cost of living crisis.