Simon Byrne has returned from a family holiday to face questions from the Northern Ireland Policing Board.
Northern Ireland’s Chief Constable will face questions later over a significant data breach.
Simon Byrne cut short a family holiday to return to Belfast to be questioned by politicians at an emergency meeting of the Northern Ireland Policing Board.
Some 10,000 Police Service of Northern Ireland (PSNI) officers and staff have been affected by the breach, which emerged on Tuesday.
The incident happened when the PSNI responded to a Freedom of Information request seeking the number of officers and staff of all ranks and grades across the organisation.
In the published response to this request a table was embedded which contained the rank and grade data, but also included detailed information that attached the surname, initial, location and departments for all PSNI employees.
The data was potentially visible to the public for between two and a half to three hours.
On Wednesday it emerged that the theft of documents, including a spreadsheet containing the names of more than 200 serving officers and staff, and a police issue laptop and radio, from a car in Newtownabbey in July, is also being investigated.
Assistant Chief Constable Chris Todd said they have contacted the officers and staff concerned to make them aware of the incident and an initial notification has been made to the office of the Information Commissioner regarding the data breach.
On Tuesday Mr Todd apologised to officers and staff over that day’s data breach, which he said was being treated as a critical incident.
He said Mr Byrne was being kept updated.
Secretary of State Chris Heaton-Harris spoke to Mr Byrne on Wednesday about the breach, which he described as a “very serious matter”.
The Police Federation for Northern Ireland (PFNI), which represents rank and file officers, said they have been inundated with calls from worried officers.
Police in the region are under threat from terrorists, with the current assessed level of threat at severe, meaning an attack is highly likely.
In February, senior detective John Caldwell was seriously injured when he was shot by gunmen at a sports complex in Co Tyrone.
Earlier this year, Mr Byrne said he receives briefings almost every day about plots to attack and kill his officers, adding that the ongoing threat from dissident republicans remains a “real worry”.
PFNI chairman Liam Kelly said there is a need for credible explanations following the breaches.
“This confirmation by the service makes matters worse,” he said of the theft of the documents and laptop.
“Urgent answers are required. How did this happen? What steps were put in place to advise and safeguard so many colleagues?
“The major security breach was bad enough, but this heaps further additional pressure on the PSNI to produce credible explanations around data security protocols and the impact on officer safety.
“Speed is of the essence. This cannot be dragged out as officers of all ranks throughout the service are seeking reassurance and an effective action plan containing all necessary measures to counter the damage and minimise risk.
“I have been inundated with calls from worried officers.
“The Police Federation has had in-depth discussions already with the PSNI senior command and they fully accept and recognise the gravity of this situation and the depth of officer anger and concern.”