Simon Byrne had faced a motion of no-confidence in his leadership from the Democratic Unionist Party (DUP).

Mr Byrne has now quit following an emergency meeting of the Northern Ireland Policing Board, which is the oversight body for the PSNI.

He had been under pressure after a data breach last month which resulted in information on about 10,000 officers and staff being accidentally disclosed online.

The breach involved the surnames, initials, rank or grade, work location and departments of all PSNI staff, but did not involve the officers' and civilians' private addresses.

The PSNI has confirmed the list is in the hands of dissident republicans, who continue to target officers.

Mr Byrne said he was "deeply sorry" for the "industrial scale breach of data that has gone into the public domain", describing it as an "unprecedented crisis".

He had on Tuesday been expected to give evidence to the Northern Ireland Affairs Committee which is investigating the breach.

A number of other data breaches have since come to light, including the loss of a police officer's laptop and notebook which contained details of 42 officers and members of staff after the items fell from a moving vehicle.

The chief constable's resignation also comes after a row erupted last week when a High Court judge ruled two junior officers were unlawfully disciplined for an arrest at a Troubles commemoration event in 2021.

The judge, Mr Justice Scoffield, said they had been disciplined to allay a threat that Sinn Fein could withdraw its support for policing.

Sinn Fein has insisted there was no such threat.

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Mr Byrne had originally said he would not quit following an emergency meeting of the Policing Board last Thursday and indicated he was considering an appeal against the court ruling.

That statement was met by anger from the Police Federation, that represents rank-and-file officers, with its chair Liam Kelly expressing "disbelief and anger" at the chief constable's remarks.

Mr Byrne had since faced growing pressure, with both rank-and-file officers and civilian staff mulling confidence votes in his leadership.

Last Friday, DUP leader Sir Jeffrey Donaldson confirmed his party had submitted a motion of no-confidence in Mr Byrne to the Policing Board.

'Policing in Northern Ireland in very difficult place'

On Monday, Sir Jeffrey said his party welcomed the chief constable's resignation.

He said: "We believe that is the right thing to do in all the circumstances and now we want to see confidence rebuilt in our police service.

"And we will work with the PSNI, they have our full support, to achieve and deliver effective and efficient policing for everyone in Northern Ireland in a way that commands cross-community support."

SDLP leader Colum Eastwood said confidence in Mr Byrne had been "irreparably shattered".

He said: "Policing in Northern Ireland is in a very difficult place right now. Successive crises have left confidence in the chief constable shattered from all directions.

"His resignation today was the right thing to do and was necessary to begin to address the serious issues facing the PSNI."