GCHQ is facing a legal challenge against its mass data collection programme in the European Court of Human Rights after three campaign groups launched proceedings this week.
Big Brother Watch, the Open Rights Group and English PEN, along with the German Internet activist Constanze Kurz, allege that GCHQ breached the privacy rights millions of people across the UK and Europe through its collection of Internet users' email communications and metadata.
The groups claim that spy agency's actions are illegal under European laws and are pushing for UK laws to be changed to remove and leeway that allows the government to collect such large volumes of data.
The challenge follows the revelation that GCHQ's Tempora programme taps into trans-Atlantic fibre optic cables to collect communications from across the world. The UK agency has the capacity to scoop up and store over 21 petabytes of data a day.
The disclosure was made by the Guardian in June based on documents leaked by whistleblower Edward Snowden, who had worked as a contractor for GCHQ's US counterpart, the NSA.
Daniel Carey, solicitor at Deighton Pierce Glynn, the firm which has taken on the case said: "We are asking the court to declare that unrestrained surveillance of much of Europe's Internet communications by the UK government, and the outdated regulatory system that has permitted this, breach our rights to privacy."
The campaigners want the European Court of Human Rights to order the UK government to tighten the Regulation of Investigatory Powers Act (RIPA), which covers surveillance and bugging.
"The laws governing how internet data is accessed were written when barely anyone had broadband access and were intended to cover old fashioned copper telephone lines," Big Brother Watch said in a statement.
"Parliament did not envisage or intend those laws to permit scooping up details of every communication we send, including content, so it's absolutely right that GCHQ is held accountable in the courts for its actions."