Stephen Fry has condemned "disgraceful" mass surveillance of communications by spy agencies GCHQ and the NSA and said it was "very depressing" how much governments wanted to control the internet.
The QI host said there was "something squalid and rancid about being spied on" and using people's fears about terrorism as a means to spy on citizens was "duplicitous and deeply wrong".
In a pre-recorded video message, Fry addressed a conference organised by the Don't Spy On Us campaign at Shoreditch Town Hall in east London to mark the first anniversary of revelations by whistleblower Edward Snowden.
Documents released by Snowden detailed a comprehensive network of web surveillance involving the US-based NSA and the UK's GCHQ, with world leaders and members of the public the victims of snooping.
In his video message, Fry, 56, said: "The idea of having your letters read by somebody, your telegrams, your faxes, your postcards intercepted, was always considered one of the meanest, most beastly things a human being could do, and for a government to do, without good cause.
"Using the fear of terrorism that we all have, the fear of the unknown that we all share, the fear of enemies that hate us, is a duplicitous and deeply wrong means of excusing something as base as spying on the citizens of your own country."
The broadcaster said GCHQ and NSA cooperated together to "read and intercept everything we send".
"It's enough that corporations know so much about us and our spending habits, our eating habits, our sexual preferences, everything else," he said.
"But that a government, something that we elect, something that should be looking out for our best interests, should presume without asking to take information that we swap, we hope privately, between ourselves is frankly disgraceful."
Fry claimed people such as him with the "highest hopes" for the internet since it started "haven't lost our optimism".
"We still think the ability to call our masters to account, to find things out, is incredibly important," he said.
"But it is very depressing how much governments wish to control the internet and it's up to us to speak out about it.
"And it's up to the real leaders and masters... the ones we trust and know are on the side of freedom, people like Sir Tim Berners-Lee (the inventor of the World Wide Web), to lend their voice to a campaign to urge governments everywhere in the free world to step back from the brink of totalitarianism that is threatening to engulf us."
Other speakers at the event included Wikipedia founder Jimmy Wales, Guardian editor Alan Rusbridger and a number of experts in technology, security and human rights.
Wales said: "The tide is beginning to turn as the public comes to understand just how broken the surveillance state is."
Snowden, a former NSA employee has since fled to Russia in order to avoid extradition to the United States, where he is facing espionage charges.
Emma Carr, acting director of Big Brother Watch, called said the UK's surveillance laws need to be reviewed. "Without affirmative action, the government will certainly find that the general public's faith in politicians to properly monitor how the security agencies are using surveillance powers will diminish," she told the Guardian.
Gos Hosein, executive director of Privacy International, added: "Secret surveillance is anathema to a democratic society, as no real debate can take place without an informed public."