London: The US National Security Agency has stored the personal electronic data of British citizens under a secret deal with London, according to files leaked by Edward Snowden and published by British media.

British officials agreed in 2007 that Britons` phone, internet and email records swept up by the NSA could be retained and analysed, instead of being off limits as was previously the case, the Guardian newspaper and Channel 4 television reported yesterday.

The revelations are the latest about apparent spying by US intelligence agencies on "friendly" countries to emerge from files leaked to the media by former NSA contractor Snowden.

The Guardian and Channel 4 cited an NSA memo from May 2007 setting out the change of policy that allows the keeping of British citizens` electronic records.

The memo states: "Sigint (signals intelligence) policy... and the UK Liaison Office here at NSAW (NSA Washington) worked together to come up with a new policy that expands the use of incidentally collected unminimized UK data in Sigint analysis."

It adds: "Now SID (the NSA`s Signals Intelligence Directorate) analysts can unminimize all incidentally collected UK contact identifiers, including IP (Internet protocol) and email addresses, fax and cell phone numbers, for use in analysis."

The deal comes despite the so-called "Five Eyes" accord between the English-speaking nations of the United States, Britain, Australia, Canada and New Zealand, under which the citizens of each country were supposedly protected from surveillance by the others.

There was no immediate reaction from US or British authorities to the latest report.

US officials want to repatriate Snowden, who is currently in Russia on temporary asylum, so he can stand trial on charges of taking and leaking classified documents about surveillance programs.

British spy chiefs said earlier that his leaks had helped Britain`s enemies.

But Snowden`s leaks have caused anger around the world at the extent of US spying, with allegations that it spied on foreign leaders - including German Chancellor Angela Merkel - straining ties with allies.