Scale and significance of NSA snooping claims
11 June 2013 Last updated at 14:42 BST
Documents leaked by former CIA worker Edward Snowden suggest that the UK data-gathering centre GCHQ has had access to a US internet monitoring programme since at least June 2010. Prism is said to give the National Security Agency and FBI easy access to the systems of nine of the world's top internet companies, including Google, Facebook, Microsoft, Apple, Yahoo and Skype.
BBC Newsnight Defence Editor Mark Urban's assessment of the NSA snooping allegations. His piece contains an interview with Edward Snowden by Glenn Greenwald/Laura Poitras/the Guardian newspaper.