In his first television appearance since claiming asylum in Russia, Snowden -- who caused shockwaves around the world by revealing mass US electronic surveillance programmes -- will give a staunch defence of privacy in the short pre-recorded broadcast.
"Together we can find a better balance, end mass surveillance and remind the government that if it really wants to know how we feel asking is always cheaper than spying," he says. Citing the classic dystopian novel "Nineteen Eighty-Four", he adds: "Great Britain's George Orwell warned us of the danger of this kind of information. "The types of collection in the book -- microphones and video cameras, TVs that watch us -- are nothing compared to what we have available today.
"We have sensors in our pockets that track us everywhere we go. Think about what this means for the privacy of the average person." Snowden, a former contractor with the National Security Agency (NSA), leaked explosive details of the secret surveillance schemes to newspapers and fled the United States. He arrived in Russia in June as a fugitive and spent more than a month holed up in a Moscow airport before being granted a year's asylum.
US federal prosecutors have filed a criminal complaint against Snowden, charging him with espionage and felony theft of government property His leaks have deeply embarrassed President Barack Obama's administration by revealing the massive scale of America's spying efforts, including on the country's own allies such as German Chancellor Angela Merkel. Snowden said a child born into today's world would "grow up with no conception of privacy at all".
"They'll never know what it means to have a private moment to themselves -- an unrecorded, unanalysed thought," he says in Wednesday's broadcast, due to be aired at 1615 GMT. "And that's a problem because privacy matters. Privacy is what allows us to determine who we are and who we want to be." He adds: "The conversation occurring today will determine the amount of trust we can place both in the technology that surrounds us and the government that regulates it."
He signs off the broadcast by wishing Britons a merry Christmas. Channel 4 has aired a short "alternative" Christmas message every year since 1993, intended as a response to Queen Elizabeth II's annual Christmas Day broadcast on the rival BBC. The channel caused a political row in 2008 when it chose former Iranian president Mahmoud Ahmadinejad as its Christmas broadcaster.
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