The UK allowed the U.S. National Security Agency to keep the mobile phone numbers and email addresses of ordinary Britons from 2007, reports say, according to BBC News.

Channel 4 News and the Guardian said existing rules were modified in 2007 to allow the U.S. to keep information swept up incidentally about Britons not suspected of criminal activity. The reports are based on documents leaked by whistleblower Edward Snowden.

The Foreign Office said it did not comment on such "speculation".

Under the seven-decade old UK-U.S. agreement on intelligence sharing, Britain and America's intelligence agencies are not supposed to collect information on each other without permission.

Before 2007, if the U.S. - on one of its other operations - had come across a British mobile phone number or email address, it would not have been able to keep it.

But, according to the documents, after the rules changed, the U.S. was allowed to keep those records to analyse them for the specific purpose of "contact chaining". That means looking at the connections between different phone numbers or email addresses.