Foreign politicians and officials who took part in two G20 summit meetings in London in 2009 had their computers monitored and their phone calls intercepted on the instructions of their British government hosts. Some delegates were tricked into using internet cafes which had been set up by British intelligence agencies to read their email traffic. The disclosure raises new questions about the boundaries of surveillance by GCHQ [Government Communications Headquarters] and its American sister organisation, the National Security Agency [NSA], whose access to phone records and internet data has been defended as necessary in the fight against terrorism and serious crime. There have often been rumours of this kind of espionage at international conferences, but it is highly unusual for hard evidence to confirm it and spell out the detail. The evidence is contained in documents - classified as top secret - which were uncovered by the NSA whistleblower Edward Snowden and seen by the Guardian. They reveal that during G20 meetings in April and September 2009 GCHQ used what one document calls ground-breaking intelligence capabilities" to intercept the communications of visiting delegations. This included: Setting up internet cafes where they used an email interception programme and key-logging software to spy on delegates' use of computers; Penetrating the security on delegates' BlackBerrys to monitor their email messages and phone calls; Supplying 45 analysts with a live round-the-clock summary of who was phoning who at the summit.