The details were inadvertently disclosed as part of the PSNI’s response to a freedom of information request about staff rank and grades, the BBC reports.

A spreadsheet containing the requested data included a second tab which revealed sensitive information about officers and staff, including which officers were assigned to units tackling paramilitarism and organised crime, or based at MI5’s Northern Ireland headquarters.

PSNI assistant chief constable Chris Todd apologised to officers for the “unacceptable” error.

He said: “We operate in an environment, at the moment, where there is a severe threat to our colleagues from Northern Ireland-related terrorism and this is the last thing that anybody in the organisation wants to be hearing this evening.

“I owe it to all of my colleagues to investigate this thoroughly and we’ve initiated that.”

Former justice minister Naomi Long, who leads the Alliance Party, said the scale of the data breach was “profoundly concerning”.

“This level of data breach is clearly of profound concern, not least to police officers, civilian staff, and their families, who will be feeling incredibly vulnerable and exposed tonight and in the days ahead,” she said.

“Immediate action must be taken to offer them proper information, support, guidance and necessary reassurances regarding their and their families’ security.

“Whilst the personal data has now been removed, once such information has been published online, it leaves an indelible footprint.

“That such sensitive information could ever have been held in a manner open to such a breach is unconscionable and will require serious investigation; however, the most urgent issue is supporting those whose security has been compromised.”