Britain's electronic eavesdropping agency GCHQ has been covertly gathering information from leading internet companies through a secret US spy programme, it has been reported.
The Guardian said that it had obtained documents showing that GCHQ had access to the Prism system, set up by America's National Security Agency (NSA), since at least June 2010.
The documents were said to show that the British agency, based at Cheltenham, had generated 197 intelligence reports through the system in the 12 months to May 2012 - a 137% increase on the previous year.
The newspaper said that the Prism programme appeared to allow GCHQ to circumvent the formal legal process required to obtain personal material, such as emails, photographs and videos, from internet companies based outside the UK.
GCHQ refused to comment directly on the report, but in a statement it insisted that it operated within a "strict legal and policy framework". "GCHQ takes its obligations under the law very seriously," the statement said.
"Our work is carried out in accordance with a strict legal and policy framework which ensures that our activities are authorised, necessary and proportionate, and that there is rigorous oversight, including from the Secretary of State, the Interception and Intelligence Services Commissioners and the Intelligence and Security Committee."
The existence of the Prism system was disclosed in earlier reports by The Guardian and The Washington Post. It followed the disclosure by The Guardian of a secret court order requiring the US telecoms company Verizon to turn over the telephone records of millions of US customers.
Details of the Prism system were said to have been set out in a 41-page PowerPoint presentation prepared for senior analysts at the NSA, the biggest electronic eavesdropping organisation in the world.
MPs expressed concern at the report. Senior Tory David Davis said it was difficult to reconcile GCHQ's statement that it was subject to proper scrutiny with the fact that Parliament had no knowledge of the programme whatsoever.
Liberal Democrat Julian Huppert, a member of the Commons Home Affairs Committee, said he hoped to force the Government to respond to an urgent question on the issue in Parliament on Monday.