Human rights groups have mounted a legal challenge following allegations that the UK’s intelligence services are spying on their own people.
Organisations including Liberty and Amnesty International are among ten groups challenging the legality of alleged surveillance operations.
The tribunal, which got underway this week, will hear claims that the intelligence and security services use a huge operation – called Tempora – to record phone calls and monitor the content of emails and other digital communications.
Ministers have refused to confirm or deny the existence of such a surveillance programme.
Liberty has claimed there is a “reasonable likelihood” that the intelligence community has interfered with private communications, in breach of the European Convention of Human Rights.
James Welch, Liberty’s legal director, argued this week that it was “neither ethical nor efficient to turn everyone into suspects.”
The Government has dismissed the allegations as “extreme, and at times outlandish”.
Allegations about Tempora first emerged in The Guardian newspaper last summer, after whistleblower Edward Snowden leaked documents from America’s National Surveillance Agency.
The papers claimed that spy agencies in Britain monitored and stored telephone and internet traffic and shared the information with their American partners.