The top government official in the British ministry responsible for policing and counter-terrorism has resigned, saying there was an orchestrated campaign to remove him.
Philip Rutnam quit after reports of tensions between him and Home Secretary Priti Patel, including allegations she mistreated officials.
Ms Patel has denied the allegations against her.
"In the last ten days I have been the target of a vicious and orchestrated briefing campaign," he told reporters.
"It has been alleged that I have briefed the media against the Home Secretary. This along with many other claims is completely false. The Home Secretary categorically denied any involvement in this campaign to the Cabinet Office. I regret, I do not believe her."
Mr Rutnam said he plans to sue for constructive dismissal
He said he had "encouraged" the Home Secretary to "change her behaviours" as his duties included "protecting the health, safety and well-being" of staff.
He went on: "My experience has been extreme but I consider there is evidence that it was part of a wider pattern of behaviour.
"I have received allegations that her conduct has included shouting and swearing, belittling people, making unreasonable and repeated demands.
"Behaviour that created fear and needed some bravery to call out."
The resignation comes after simmering tensions between Ms Patel and her Permanent Secretary boiled to the surface last weekend with various reports about a rift between the two.
Mr Rutnamp made light of those reports when he made he appeared at a police summit in London on Thursday.
But he made clear his feelings in his statement this morning, which he read to the BBC outside an address in north London.
He said he took the decision to quit "with great regret after a career of 33 years" and said he would be issuing a claim against the Home Office for constructive dismissal.
Additional Reporting PA