The first major challenge to the legality of UK intelligence agencies intercepting private communications in bulk is due to be heard by the European Court of Human Rights (ECHR), in three separate cases brought by civil rights groups, including Liberty, Amnesty International, Privacy International and the American Civil Liberties Union.
Seven judges in Strasbourg will consider the cases, which raise serious questions about the way GCHQ, MI5 and MI6 share surveillance material with the US and other foreign governments.
One of the claims, brought by an alliance of 10 human rights organizations, has already been considered by the investigatory powers tribunal in London, which took some evidence in secret and ruled that the UK surveillance regime had been unlawful, as it breached the right to privacy under Article 8 of the European Convention on Human Rights, but was now compliant.
Nonetheless, the same tribunal found that the GCHQ spied on rights group Amnesty International and South African non-profit Legal Resources Center, retaining and illegally examining their data.
The other two claims at Strasbourg, brought by Big Brother Watch and the Bureau of Investigative Journalism, allege government interception breaches freedom of expression and the right to a fair trial, on the grounds that Investigatory Powers Tribunal hearings do not provide an effective domestic remedy, as they are held partially in secret.
All the groups involved also argue that if their communications have been spied on, the confidentiality and protection of vulnerable sources and informants with whom they regularly deal will have been jeopardized.
"This case is a watershed moment for privacy and freedom of expression across the world. The case concerns the UK, but its significance is global. It also serves to highlight the dangers mass surveillance poses to the vital work of countless organisations and to individuals who expose human rights abuses and defend those at risk," said Nick Williams, Amnesty International's Senior Legal Counsel.
In particular, the case challenges the legality of the indiscriminate surveillance of UK citizens and the bulk collection of vast amounts of personal information and communications by UK intelligence agencies under the legal regime set out in the Regulation of Investigatory Powers Act (RIPA) 2000.
The UK surveillance regime under RIPA was untargeted, meaning UK citizens' private communications and information was collected at random without suspicion or evidence of wrongdoing. Moreover, no authorization was required for the interception of the communications and the process of interception was effective indefinitely.
"We are challenging the RIPA regime on the grounds there was no sufficient legal basis for such indiscriminate bulk interception, no defined limits on the exercise of the power and no adequate oversight — therefore, it infringed UK citizens' right to a private life. Specifically, our case questions whether; the storage and searching of those intercepted communications is lawful; the use of computer programs to search this data is an interference with people's privacy; greater controls are needed so it doesn't circumvent UK safeguards; and [if it's] fair there are different standards applied to UK and non-UK residents," Big Brother Watch said in a statement.
However, the hearings will also focus on bulk interception programs revealed by Edward Snowden in 2013, including Tempora, Upstream and Prism.
Tempora enabled the GCHQ to intercept and store a backup of internet activity entering and leaving the UK via fiber optic cables for subsequent inspection; Upstream allowed the US National Security Agency to carry out similar operations in the US; Prism permitted the NSA to access communications passing through US companies such as Microsoft, Apple, Yahoo!, Google, Facebook, Skype and YouTube.
GCHQ has sought to defend its practices by making a distinction between "mass surveillance" — which the agency insists it does not undertake — and "bulk interception" of communications, which it alleges is necessary to carry out targeted searches of data in pursuit of terrorist or criminal activity.
The eventual judgement could have implications for 2016's controversial Investigatory Powers Act, which changed the UK's legal framework governing surveillance.
"Our organizations exist to stand up for people and challenge abuse of power. We work with whistleblowers, victims, lawyers, journalists and campaigners around the world, so confidentiality and protection of our sources is vital. The UK Government's vast cross-border mass surveillance regime — which lets it access millions of people's communications every day — has made those protections meaningless," said Martha Spurrier, the director of Liberty.
She added that the loss of privacy was a "gateway to losing everything that keeps us free," such as the right to protest, fair trials, the practicing of religion and thinking and speaking freely.