Legal action has been formally launched against Priti Patel following allegations of bullying from a top civil servant.
Sir Philip Rutnam, who was the Home Office's permanent secretary, quit in February amid criticism of Ms Patel's alleged behaviour.
He is claiming “constructive dismissal” and submitted a claim to an employment tribunal on Monday morning, civil servants’ union the FDA said.
Ms Patel expressed concern at the “false” claims against her and allies described her as a “demanding” boss but not a bully.
In a statement, FDA general secretary Dave Penman said: “On 29 February 2020, Sir Philip Rutnam resigned as permanent secretary of the Home Office, indicating that he intended to pursue a claim of constructive dismissal.
“Following his resignation, the FDA instructed Gavin Mansfield QC, head of Littleton Chambers and employment law specialist, as counsel to advise Sir Philip, supported by Clive Howard, senior principal lawyer, employment and partnership at Slater and Gordon.
“This morning, Sir Philip, with the support of his legal team and the FDA, submitted a claim to the employment tribunal for unfair (constructive) dismissal and whistleblowing against the Home Secretary."
It is understood the papers have been lodged at the Central London Employment Tribunal and the latest move in his legal case comes as the Cabinet Office is expected to conclude an inquiry into claims against Ms Patel.
She has been accused of clashing with senior officials and belittling colleagues.
When he quit Sir Philip was highly critical of Ms Patel, claiming he had been the target of a “vicious and orchestrated briefing campaign” which he accused her of orchestrating, and said the decision to resign was with “great regret after a career of 33 years”.
