The chief executive of Cambridgeshire and Peterborough Combined Authority has quit after less than a year amid a bullying probe into the mayor.

A formal code of conduct investigation into Labour Mayor Nik Johnson by an external investigator is understood to be underway after a complaint was submitted by a whistleblower.

Tensions between chief executive Eileen Milner and Mayor Johnson have threatened to erupt for months but attempts at mediation came to an end before her resignation.

In a letter to the combined authority board, Ms Milner, a former civil servant, cited the whistleblowing investigation when explaining her reasons for quitting.

In her letter, Ms Milner, who was formerly chief executive of the Education and Skills Funding Agency, said the ‘negative impact of the last few months upon my own health and wellbeing' has meant it was ‘simply not possible' for her to remain in her role.

The Department for Levelling Up, Housing and Communities has been informed about the reasons behind Ms Milner's resignation but if the Government decides to intervene legislation does not allow it to appoint commissioners.

A number of elected members on the combined authority board have become increasingly unhappy about the conduct of the mayor and have signed a ‘requisition' calling for Mayor Johnson to ‘consider either resigning' or ‘voluntarily suspending himself' while investigations are ongoing.

The requisition – dated 19 April – said that if the mayor had neither resigned nor voluntarily suspended himself within seven days of the motion the board ‘shall be deemed to have passed a motion of no confidence in the mayor'.

Responding to the motion, Mayor Johnson agreed to call a meeting of the combined authority, but election rules mean this can only occur after today.

A combined authority spokesperson confirmed Ms Milner had given notice of her resignation but said: ‘We do not comment publicly on matters relating to member conduct unless and until they have reached the outcome stage.

'We do not comment publicly on ongoing whistleblowing matters.'