British spooks went to elaborate lengths to spy on members of the G20 summit when it was held in the UK in 2009.
Apparently GCHQ intercepted foreign politicians' communications at G20 summits, monitored phones and set up fake internet cafes to gather information from allies.
Among the pile of documents leaked by NSA whistleblower, Edward Snowden, there was information on the surveillance of G20 delegates' emails and BlackBerrys.
According to the Guardian, 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.
This news is probably the last thing that the British government wants to leak out, just as the nation prepares to host another summit for the G8 nations today.
After all it is not a good idea that all your guests know they were the object of the systematic spying the last time they turned up.
Visiting delegates who will want the prime minister to explain whether they were targets in 2009 and whether the exercise is to be repeated this week.
The G20 spying appears to have been organised for the more mundane purpose of securing an advantage in meetings. Named targets included South Africa and Turkey.
This is the first time that there has been hard evidence to confirm that international conferences are targets for spies. It had been long suspected, but never proved.
Snowden's leak 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.
MI6 hacked the security on delegates' BlackBerrys to monitor their email messages and phone calls;
More than 45 analysts were provided with a real-time summary of who was phoning who at the summit.
The system targeted the Turkish finance minister and possibly 15 others in his party,
Meanwhile the British spooks were receiving reports from an NSA attempt to eavesdrop on the Russian leader, Dmitry Medvedev, as his phone calls passed through satellite links to Moscow.
It was all approved at a senior level in the government of the then prime minister, Gordon Brown, and that intelligence, including briefings for visiting delegates, was passed to British ministers.
One document refers to a tactic which was "used a lot in recent UK conference, eg G20".
This involves an active collection against an email account that acquires mail messages without removing them from the remote server.
A PowerPoint slide explains that this means "reading people's email before/as they do" just in case you were a minister and did not know what that meant.