Rishi Sunak still has confidence in his deputy after an inquiry into Dominic Raab’s behaviour was expanded to include a third formal complaint lodged against him.
The latest claim relates to Mr Raab’s tenure in the now-defunct Department for Exiting the European Union, Downing Street said.
No 10 said it is understood the most recent allegation was received by the Cabinet Office on Wednesday.
Mr Sunak asked for the scope of the inquiry to be updated on Thursday night, having received the “requisite advice” from the department.
Asked if Mr Sunak still had confidence in Mr Raab, she said: “Yes, he does.
“There’s now an independent investigation that’s ongoing. It’s led by someone with extensive experience in this area. We’re not going to pre-empt or pre-judge that process.”
Deputy Labour leader Angela Rayner demanded the scope of the investigation be expanded to “enable proactive investigation” into Mr Raab’s conduct.
“The drip-drip-drip of serious complaints emerging about his Deputy shows he can no longer stem the tide,” she said.
“Rishi Sunak’s attempted stitch-up will fool no one.”
It comes after a source confirmed on Thursday that multiple senior officials who worked closely with Mr Raab were preparing to submit further formal complaints, as first reported by BBC’s Newsnight.
The allegations, if lodged, could be included in the investigation being carried by senior lawyer Adam Tolley KC.
Mr Raab requested the independent inquiry last week after two bullying complaints were lodged against him.
The Lib Dems have warned the “flood of allegations” about Mr Raab’s behaviour cannot be “swept under the carpet”.
The party’s chief whip, Wendy Chamberlain, said: “Rishi Sunak must confirm he will sack Raab if these complaints are upheld.”