Lisa Nandy has claimed that bullying allegations surrounding Dominic Raab were an “open secret” in Westminster.
The Labour frontbencher said she heard a number of rumours about Raab when he was foreign secretary and she shadowed him.
It comes amid claims from civil servants that the deputy prime minister bullied staff.
The allegations relate to his previous stint as justice secretary under Boris Johnson, with staff reportedly offered a “route out” of his department when he was reinstated in October.
Nandy, shadow levelling up secretary, told Sky News: “I have to say that when I was shadow foreign secretary - opposite Dominic Raab as foreign secretary - I did hear a number of rumours that this was a pattern of behaviour within the department.
“I think it’s been something of an open secret within Westminster for the last few years that there is a problem.
“There was a problem in the justice department, there was a problem in the foreign office, and it was particularly apparently directed towards women.
“This is something that we hear coming out over and over again with this government that there are accusations of bullying from the civil servants.”
Nandy suggested people who were not in positions of power feel they cannot speak openly due to the repercussions.
She said it was “damning” that Rishi Sunak appointed him to the post and pointed to other allegations surrounding Gavin Williamson and Priti Patel.
“There just seems to be a real rot at the heart of this government and it doesn’t seem to have shown any signs of abating under the new prime minister,” Nandy added.
The prime minister has defended Raab, saying he does not recognise the characterisation.
Sunak told journalists: “I don’t recognise that characterisation of Dominic and I’m not aware of any formal complaints about him.
“Of course there are established procedures for civil servants if they want to bring to light any issues. I’m not aware of any formal complaint about Dominic.”
However, Simon McDonald, the former permanent secretary at the foreign office when Raab, has suggested that bullying claims were accurate.
Civil servants who worked with Raab told The Guardian he was a “very rude and aggressive” boss while another report claimed the justice secretary had acquired the nickname “The Incinerator” because he “burns through” staff.
He was also accused in The Sun of hurling tomatoes across a table in a fit of rage. His spokesman described the claims by anonymous sources as “complete nonsense”.
Raab is expected to be asked about the allegations when he stands in at prime minister’s questions tomorrow.
A spokesperson for Raab said: “The deputy prime minister has worked in government for over seven years as a minister or secretary of state across four departments and enjoyed strong working relationships with officials across Whitehall.
“He consistently holds himself to the highest standards of professionalism and has never received nor been made aware of any formal complaint against him.”