Thousands of people are signing up to join an unprecedented legal campaign against the United Kingdom’s leading electronic surveillance agency.

On Monday, London-based human rights group Privacy International launched an initiative enabling anyone across the world to challenge covert spying operations involving Government Communications Headquarters, or GCHQ, the National Security Agency’s British counterpart.

The campaign was made possible following a historic court ruling earlier this month that deemed intelligence sharing between GCHQ and the NSA to have been unlawful because of the extreme secrecy shrouding it.

Consequently, members of the public now have a rare opportunity to take part in a lawsuit against the spying in the Investigatory Powers Tribunal, a special British court that handles complaints about surveillance operations conducted by law enforcement and intelligence agencies.

Privacy International is allowing anyone who wants to participate to submit their name, email address and phone number through a page on its website. The group plans to use the details to lodge a case with GCHQ and the court that will seek to discover whether each participant’s emails or phone calls have been covertly obtained by the agency in violation of the privacy and freedom of expression provisions of the European Convention on Human Rights. If it is established that any of the communications have been unlawfully collected, the court could force GCHQ to delete them from its vast repositories of intercepted data.

By Tuesday evening, more than 10,000 people had already signed up to the campaign, a spokesman for Privacy International told The Intercept.

In a statement announcing the campaign on Monday, Eric King, deputy director of Privacy International, said: “The public have a right to know if they were illegally spied on, and GCHQ must come clean on whose records they hold that they should never have had in the first place.

“We have known for some time that the NSA and GCHQ have been engaged in mass surveillance, but never before could anyone explicitly find out if their phone calls, emails, or location histories were unlawfully shared between the U.S. and U.K.

“There are few chances that people have to directly challenge the seemingly unrestrained surveillance state, but individuals now have a historic opportunity finally hold GCHQ accountable for their unlawful actions.”

Details about the scope of GCHQ and NSA surveillance first emerged in June 2013 following leaks from NSA whistleblower Edward Snowden, which exposed a series of major secret programs used to sweep up private communications on a large scale. Last year, The Intercept revealed new details about GCHQ’s efforts to push for broader access to data swept up by the NSA.

GCHQ declined to comment about the Privacy International initiative, and referred inquiries from The Intercept to the British government’s Home Office. A Home Office spokesperson said in emailed statement:

The current regime governing both the intelligence agencies’ external interception and intelligence sharing regimes is lawful and European Court of Human Rights compliant. This government is committed to transparency. It has made public more detail than ever before about the work of the security and intelligence agencies, including through the publication of statutory codes of practice. We have now made public the detail of the safeguards that underpin requests to overseas governments for support on interception.

Photo: A Banksy artwork near GCHQ headquarters in Cheltenham, England: Matt Cardy/Getty Images.

