A secret data breach has exposed the identities of over 100 British special forces personnel and intelligence officers, alongside thousands of Afghan nationals who worked with the UK during the war in Afghanistan, putting them at serious risk.

The full extent of the February 2022 breach had been hidden under court orders until this week, when a High Court judge partially lifted restrictions, allowing media to reveal that names of MI6 and Special Air Service members were contained in the leaked database.

The government had earlier acknowledged that nearly 19,000 Afghan applicants to the UK relocation scheme had their personal details mistakenly disclosed.

Many of them had cooperated with British forces during the 20-year conflict, making them potential targets for Taliban revenge attacks.

The leak, which remained undetected until August 2023, only came to light when a person in Afghanistan who had obtained the data posted a portion on Facebook and threatened to release more.

The Ministry of Defence (MoD) responded by fast-tracking the person’s relocation to the UK in what sources described as a move driven by “essentially blackmail”.

Although the MoD did not confirm this claim, it stated that anyone entering the UK under Afghan relocation programmes is subject to strict security vetting.

The breach reportedly began when an official at the UK Special Forces headquarters in London mistakenly emailed over 30,000 resettlement files to an unauthorised individual, believing the transmission included information on just 150 applicants.

The individual outside government later published some of the data online, prompting concern for those still living in Afghanistan.

The UK government quietly created the Afghanistan Response Route (ARR) after discovering the breach.

This special scheme has since resettled around 4,500 affected Afghans and their families, with an additional 2,400 expected to arrive in the UK, pushing the cost of the operation to at least £850 million. However, those affected were never told about the breach, despite the potential dangers.

After Tuesday’s lifting of the super-injunction that had initially prevented reporting of the leak altogether, a secondary legal order still blocked media from naming the compromised British security personnel.

That restriction was lifted Thursday, following an agreement between the MoD and a coalition of news organisations, allowing further reporting.

Defence Secretary John Healey labelled the breach a “serious departmental error” and acknowledged that it was one of several data losses connected to Afghan relocation efforts.

The opposition's shadow defence secretary, James Cartlidge, apologised in Parliament on behalf of the previous administration, under whose watch the breach occurred.

The Taliban has denied targeting or detaining those named in the leak, but Afghan relatives interviewed by the BBC said they fear the information has made their families more vulnerable.

One said Taliban efforts to locate their relative intensified after the breach.

The MoD has refused to disclose whether anyone has been harmed as a result of the exposure. A spokesperson said, “It's longstanding policy of successive governments to not comment on special forces.

We take the security of our personnel very seriously, particularly of those in sensitive positions, and always have appropriate measures in place to protect their security.”