SIR Stephen House has announced he is to quit early as Police Scotland chief constable after vowing that the single force will learn from any mistakes made.

Sir Stephen is to leave the force three years after becoming the country's most senior policeman.

He had previously planned to go at the end of his four-year contract in September next year, but has now decided to leave within months after a series of recent controversies.

These include the M9 crash in which police failed to attend the scene for three days despite receiving a call reporting it, and the death in custody of Sheku Bayoh who died after being restrained by officers during an incident in Kirkcaldy.

There have also been rows over the alleged spying on journalists’ sources by the force and non-statutory stop and searches.

He referred to the M9 and Sheku Bayoh cases at a meeting of the Scottish Police Authority (SPA) where he announced the decision yesterday.

An emotional Sir Stephen said: "I also want to give my sincere commitment that where mistakes have been made, we will learn from those mistakes, and any recommendations which will improve the performance of Police Scotland in relation to incidents like this will be taken on board without question."

He expressed his frustration that he is unable to answer his many critics on the incidents which have led to waves of negative publicity for the force.

Sir Stephen told members of the SPA in Stirling he could not update them on the matters.

"Every death, quite clearly, is a tragedy for the families and the friends of the victims.

"I cannot begin to understand, and I don't think anyone who has not been directly affected can begin to understand what these families are going through, and we don't pretend that we do.

"But I can give my assurance on behalf of the organisation that we continue to repeat our condolences to all those who have been affected by the tragedies.

He added: "We would like to give full and frank answers to the questions that are legitimately being asked, but we are unable to do that because there are independent investigations being run."

Embattled Sir Stephen decided enough was enough after returning from a holiday with his family.

He was named the chief constable of Strathclyde Police in October 2012 and also chief constable of Police Scotland which was formally established in April 2013.

He had previously said he would go at the end of his four-year contract in September next year, but claimed he now felt "the time is right for me to try to take up new challenges and to allow the start of the process to recruit my successor".

The new head of the force has been tipped to come from within.

A policing source said the new chief constable is likely to be an internal candidate because the Scottish Government will look to appoint "someone they know and trust".

Senior officers Deputy Chief Constable Iain Livingstone, currently in charge of crime and operational support at the force, and Deputy Chief Constable Rose Fitzpatrick, currently in charge of local policing, are thought to be the main contenders for the top role.

SPA chair Vic Emery, who will also stand down at the end of next month, said the authority would start to put the recruitment process in place "in the coming days", but added it would be completed by his successor, who will be announced imminently.

DCC Livingstone, one of the favourites to secure the force's top job, began his career at Lothian and Borders Police in 1992 and rose through the ranks to become Assistant Chief Constable before being appointed as a deputy in the new single force at its outset.

A highly placed policing source described him as having an "empathy and understanding that Mr House lacked".

DCC Fitzpatrick, who was awarded the Queen's Police Medal in 2007, was brought into the new single force as a deputy after serving as a Deputy Assistant Commissioner with the Met.

The other officers in the running include Sir Stephen's second in command, Deputy Chief Constable Neil Richardson, and Deputy Chief Constable Steve Allen, currently in charge of major events at the force.

Chief Superintendent Niven Rennie, president of the Association Scottish Police Superintendents, said the recent criticism directed at the chief had taken its toll.

Mr Rennie said: "What we've had is one individual at the top of the structure being the subject of all the criticism.

"Steve House is human like us all and can only take so much. He's a strong and principled person but that barrage of sustained criticism has taken its toll.

"He's spent two weeks with his wife and family on holiday and this would've been uppermost in his mind and most likely where and when he's made his decision to quit early."

However, the source claimed his departure was also prompted by the start of the new Holyrood parliamentary session, next week, when a series of problems will come under renewed scrutiny.

Labour councillor Paul Rooney, who was a key figure in bringing Sir Stephen to Scotland from the Met, also put the Chief Constable’s departure in the context of the recent problems engulfing his force.

SPA member Mr Rooney said: "In my years within policing, I do not recall such a turbulent time as in recent months with two significant tragedies. However, I believe Sir Stephen's personal determination and professionalism to address the issues behind these incidents has been honourable."

Sir Stephen thanked his officers and staff as he made his announcement and said he was confident any future challenges would be met due to their quality and dedication.

He said the force has achieved a lot since its inception in 2013, including "a new national approach to domestic abuse and sexual attacks, the ending of a postcode lottery approach to specialist services, and an improved ability to deal with major incident and events".

The police chief added: "I'm immensely proud to have been the first chief constable of Police Scotland and to lead the men and women in it, but for me the time has come to move on and take up new opportunities."