Edward Snowden leaks: UK 'let NSA store email addresses'
21 November 2013 Last updated at 01:55 GMT
The UK allowed the US National Security Agency to keep the mobile phone numbers and email addresses of ordinary Britons from 2007, according to media reports.
The reports are based on documents leaked by whistleblower Edward Snowden.
The Foreign Office said it did not comment on such "speculation".
BBC Security Correspondent Gordon Corera reports.