Professor Susan Deacon has resigned as chair of the Scottish Police Authority.

Deacon informed the watchdog's board members at a meeting yesterday and quit in a letter to Justice Secretary Humza Yousaf.

On the second anniversary of her appointment, she told the board she had taken the SPA as far as she could, but believes there are deep-rooted flaws in the system and it needs to be reformed.

Her resignation comes just 48 hours after Gill Imery, HM Chief Inspector of Constabulary in Scotland, said the organisation was not doing "particularly well at the moment" in its key functions of holding Police Scotland to account and advocating for the force.

Ms Imery told Holyrood's Justice Committee on Tuesday that senior officers at Police Scotland had become "frustrated" by the lack of scrutiny.

In September, a report into governance at the SPA highlighted a "damning culture of failure".

In her letter to Yousaf, Prof Deacon said she had "worked tirelessly" but urged the Scottish Government to think "afresh" about how the watchdog operates.

She wrote: "I consider it a privilege to have played a part in developing and strengthening policing in Scotland and I am pleased that I leave this role with our police service in a much stronger place than it was when I was first appointed, exactly two years ago.

"I have, as you have frequently acknowledged, worked tirelessly to try and ensure that the SPA operates effectively, and that public confidence and trust in policing is maintained. I have also made every effort to attempt to make the existing statutory framework operate as I believe it was intended.

"In truth, however, I have increasingly become convinced that the governance and accountability arrangements for policing in Scotland are fundamentally flawed, in structure, culture and practice, and I conclude that there is little more I can do to make these arrangements work effectively.

"I would suggest that the Scottish Government thinks afresh about how the police service is scrutinised and held to account and how, or if, a better separation between politics and policing, and indeed between the police service and those who oversee it, can be achieved.

"I would be pleased to share my thoughts and reflections on these matters with you, and indeed with the Scottish Parliament's justice committee, at any time.

"May I thank you for the opportunity to have served in this role and hope that our police service continues to develop effectively in the future."

Deacon was a Labour MSP for Edinburgh East and Musselburgh between 1999 and 2007 and is a former health minister. When she took up the SPA role in December 2017, then justice secretary Michael Matheson said she would "bring a fresh perspective to the governance of Scottish policing".

However, the September report from HM Inspectorate of Constabulary in Scotland (HMICS) found that the chair and a number of board members at SPA were acting "well outwith their core non-executive roles", contrary to their agreed job descriptions and guidelines.

The report also noted there was "no clear vision, strategy or plan in place" for the SPA, which has resulted in a lack of wider understanding of the steps required to achieve its aims.

Vice-chair David Crichton will take on the role until a permanent new chair is appointed.

He said: "The members of the authority wish to acknowledge the significant contribution that Susan Deacon has made as chair of the SPA over the past two years.

"She took up the role at a period of considerable instability in the police service. That Police Scotland now has a strong, resilient leadership team in place is testimony to her contribution to the improvement of policing in that period.

"We believe that the system of governance and accountability for policing in Scotland that was envisaged by the founding legislation is a sound one and can work effectively."

Ms Deacon's resignation comes three months after Hugh Grover stepped down as chief executive of the SPA after being off ill since May this year.