A police officer lost his laptop and notebook as he drove along the motorway after leaving them on the roof of his car - in the fourth data breach by a single force.

The PSNI said it is investigating after a senior officer revealed sections of the lost notebook remain outstanding.

The latest revelation comes just a week after the force suffered a major data breach when the personal details of more than 10,000 officers and staff were mistakenly released.

Assistant Chief Constable Chris Todd said: 'It is believed the material fell from a moving vehicle on the foreshore stretch of the M2 motorway on Thursday August 17, around 4.15pm.

'The laptop was immediately deactivated and has been recovered. Sections of the notebook remain outstanding.

A police officer lost his laptop and notebook as he drove along the motorway after leaving them on the roof of his car. This is the fourth data breach by a single force (File image)

'Inquiries are under way to establish the contents of the notebook.'

They added: 'We will be liaising with the Office of the Information Commissioner and have advised the Northern Ireland Policing Board and the Department of Justice.

'Anyone with information or who recovers any material is asked to contact police on 101.'

Meanwhile, a man has been arrested in Co Londonderry by detectives investigating potential criminality linked to last week's major data breach.

The 50-year-old was detained under the Terrorism Act following a search in the Dungiven area on Friday. He is being questioned at Musgrave Serious Crime Suite in Belfast.

Detective Chief Superintendent Andy Hill said officers are investigating the sharing of information from the data breach.

He said: 'We continue to work toward establishing those who possess information relating to last week's data breach, and will take action to ensure that any criminality identified is dealt with robustly to keep communities, and our officers and staff who serve them, safe.'

Earlier this week, a 39-year-old man was detained following a search in Lurgan, Co Armagh, as part of the same investigation.

The latest revelation comes just a week after the force suffered a major data breach when the personal details of more than 10,000 officers and staff were mistakenly released (File image)

He was questioned on suspicion of collection of information likely to be of use to terrorists, and later released on bail to allow for further police inquiries.

Last week the PSNI revealed a document had mistakenly been shared online in response to a freedom of information request.

Details released included the surname and first initial of every employee, their rank or grade, where they are based and the unit they work in.

This week PSNI Chief Constable Simon Byrne said he believed the information was in the hands of dissident republicans.

It followed the posting of documents from the leak on a wall near a Sinn Fein office in Belfast.

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Many officers have expressed concern for their safety in Northern Ireland, where police are under threat from terrorists - with the current level of threat assessed as severe, meaning an attack is highly likely.

Earlier this year, dissident republicans were blamed for the attempted murder of senior PSNI detective John Caldwell.

The Policing Board, which has oversight of the PSNI, is to hold a follow-up meeting next Tuesday to receive an update on the data leak and to consider further actions necessary.

A spokesperson said: 'Members will also have the opportunity to question other data loss incidents that have been reported over the course of the last week.'

Last week the PSNI also revealed that in a separate incident, a document containing the names of officers and staff was stolen along with a police-issue laptop from an officer's car on July 6.

The Northern Ireland Policing Board is to hold an additional meeting over last week's major PSNI data breach

A spokesperson for the board, which oversees policing in the region, said members will receive an update from PSNI Chief Constable Simon Byrne and consider any further actions necessary.

'The Northern Ireland Policing Board will hold a follow-up meeting on Tuesday August 22 with the chief constable to receive an update on issues arising from the August 8 data breach and consider any further actions necessary,' they said.

'Members will also have the opportunity to question other data loss incidents that have been reported over the course of the last week.'