Rishi Sunak is facing growing questions over his judgement after reports a minister he appointed to the cabinet last week is embroiled in allegations of misconduct.
Labour’s Deputy Leader Angela Rayner called for an “urgent” investigation.
The allegations, against cabinet minister Gavin Williamson, were reported by the media organisation Tortoise.
Ms Rayner said: "These new revelations raise fresh questions about Rishi Sunak’s woeful judgment in resurrecting ministers who left government under a cloud of misconduct.
“Gavin Williamson was sacked from cabinet twice, yet despite risking national security he has now been put at the heart of the government’s corporate headquarters.
"Given his 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."
Mr Williamson left Theresa May’s government amid claims of a security breach. A Conservative Party spokesperson said the party had “a robust complaints process in place”.
A friend of Williamson also told Tortoise “strongly refutes these allegations” and is “very happy to share all communications with the former chief whip with CCHQ if needed”.
Mr Williamson has been approached for comment.
Himself a former chief whip, he played a key role in the prime minister’s leadership campaign this summer.
He was made minister without portfolio after Mr Sunak took the top job in the wake of Ms Truss’s resignation.
The return of Mr Williamson was widely seen as an extraordinary political comeback. He has twice been sacked from the cabinet.
Once when he was defence secretary under Ms May and again by Boris Johnson when as education secretary he was blamed for the pandemic exams fiasco.
Mr Sunak is already facing questions over his decision to appoint Suella Braverman to his first cabinet.
He reappointed her to the position of home secretary just days after she resigned from the post over a breach of the ministerial code.
She was also roundly condemned after she claimed the UK was facing an “invasion” of migrants on its south coast.
Charities accused her of dehumanising language that would put public safety at risk.
Ms Braverman made her comments just 24 hours after a firebomb attack on an immigration centre in Dover.
The embattled cabinet minister has also come under fire for the overcrowding crisis at an asylum centre in Kent.
As the controversy over his choice of home secretary raged, Mr Sunak told the Commons earlier this week they were “on the same page”.
But he declined to say whether she had been given legal warnings about blocking the transfer of asylum seekers from the centre in Manston into hotels.
He was also forced to admit that “not enough” asylum claims had been processed, but insisted: “That’s what we are going to fix.”
But he was warned by a leading polling expert that the reappointment of Ms Braverman could blow a hole in his hopes of holding onto power at the general election.
Sir John Curtice said restoring Ms Braverman after just six days to the post she lost due to a breach of the ministerial code represented a “risk”.
