Official figures have revealed that in Britain each day last year, local authorities, police and the intelligence services had granted more than 1,500 requests to snoop on the public's phonecalls, emails and text messages.
Nearly 10,000 such applications were made each week of 2008, making a total of 504,073 requests for communication data.
The figures were published in the annual report of the Interception of Communications Commissioner, Sir Paul Kennedy. The bodies were allowed access to records of phone, email and text messages but not their content.
The Regulation of Investigatory Powers Act allows bodies such as local authorities to ask for the private data. The Act is now coming under threat from opposition parties.
Lib Dem home affairs spokesman Chris Huhne told the Press Association: "Many of these operations carried out by the police and security services are necessary, but the sheer numbers are daunting.
"It cannot be a justified response to the problems we face in this country that the state is spying on half a million people a year.
"We have sleepwalked into a surveillance state but without adequate safeguards. Having the Home Secretary in charge of authorisation is like asking the fox to guard the hen house.
"The Government forgets that George Orwell's 1984 was a warning, and not a blueprint. We are still a long way from living under the Stasi but it beggars belief that it is necessary to spy on one in every 78 adults. The fact that numbers are up a half on two years ago makes a mockery of the Government's supposed crackdown."