Last updated at 13:17 01 June 2007

In a bunker beneath the bustling streets of central London, guards monitor a grid of closed-circuit television.

The centre, at a secret location, is run by a private company in association with the police and local council.

Polls show broad public acceptance, even if the cameras more often capture a couple in loving embrace than a terrorist about to wreak havoc.

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Britain has more than 4 million closed-circuit security cameras, more than any other Western democracy.

Police say the average Briton is on as many as 300 cameras every day, usually unaware.

The density of surveillance is significantly higher than in any other Western democracy, says Jen Corlew, spokeswoman for Liberty, a London-based human rights group.

"We are sleepwalking towards a Big Brother society, not in one fell swoop but by stages," warns The Spectator, a conservative magazine.

"There is no boot stamping on a face: just an ever more insistent foot in the door."

But the vast majority of 4,000 people surveyed in 2005 said they believed that tapping phones, opening mail and following terror suspects were a price worth paying to stay safe, according to British Social Attitudes Report - an annual survey released in January.

Some 81 percent thought tapping telephones and opening mail were prices worth paying. For terrorism suspects, 80 percent supported electronic tagging.

The British seem to have rallied around the idea that some long-accepted freedoms may have to be curbed in the face of a common enemy - in much the way an earlier generation made sacrifices during World War II.

"When it comes to people's safety, I don't think they can go too far," said Jonathon Walkes, 29, a London lawyer.

"For the most part, we just go about our lives knowing that people are watching. I'm still rowdy after a night at the pub."

British authorities say people shouldn't worry about the close surveillance - unless they're doing something wrong.

"We appreciate that the cameras and some of the other measures are seen as invasive, but only people who really have something to worry about should be concerned," David Morgan, a Metropolitan Police Chief Superintendent, said on a tour of the bunker.

As he spoke, a series of seemingly private moments unfolded - ranging from a young couple stepping into the shadows for a kiss to a driver sneaking into a restricted bus lane.