British officials have given their word: "We won't read your emails."
But experts say the government's proposed new surveillance program will gather so much data that spooks won't have to read your messages to guess what you're up to.
The U.K. Home Office stresses it won't be reading the content of every Britons' communications, saying the data it seeks "is NOT the content of any communication."
It is, however, looking for information about who's sending the message and to whom, where it's sent from and other details, including a message's length and its format.
The proposal, unveiled last week as part of the government's annual legislative program, is just a draft bill, so it could be modified or scrapped. But if passed in its current form, it would put a huge amount of personal data at the government's disposal, which it could use to deduce a startling amount about Britons' private lives -- from sleep patterns to driving habits or even infidelity.
"We're really entering a whole new phase of analysis based on the data that we can collect," said Gerald Kane, an information systems expert at Boston College. "There is quite a lot you can learn."
The ocean of information is hard to fathom. Britons generate 4 billion hours of voice calls and 130 billion text messages annually, according to industry figures.
In 2008, the BBC put the annual number of U.K.-linked emails at around 1 trillion.
Then there are instant messaging services run by companies such as BlackBerry, Internet telephone services such as Skype, chat rooms, and in-game services like those used by World of Warcraft.
Communications service providers, who would log all that back-and-forth, believe the government's program would force them to process petabytes (1 quadrillion bytes) of information every day.
It's a mind-boggling amount of data, on the scale of every book, movie and piece of music ever released.
British officialdom has been pushing for a mass surveillance program for years. But civil libertarians are perturbed, branding the proposal a "snooper's charter."
Kane says the surveillance regime has to be seen in the context of social networks such as Facebook and LinkedIn, where hundreds of millions of people are constantly volunteering information about themselves, their friends, their family and their colleagues.
"There's no sense in getting all Big Brother-ish," he said. "The bottom line is that we're all leaving digital trails, everywhere, all the time. The whole concept of privacy is shifting daily."