Nicholas Clegg, the new deputy Prime Minister of the United Kingdom, and one half of that country's power-sharing coalition, has set the bar high for his political reform agenda. In a speech Wednesday in north London, Clegg unveiled what he called "a power revolution, a fundamental resettlement of the relationship between the state and the citizen..." And to kick it off, he took aim at the U.K.'s pervasive security apparatus, a network of thousands of video cameras, a national DNA database, and an aggressive domestic intelligence service. Clegg's speech was full of rhetorical flourish, but if he's serious, and if he makes good on his plans, it will indeed mark a fundamental shift in the constant tension between security and personal liberty, and it could have consequences on this side of the pond.

Supporters of enhanced surveillance must offer a better argument for why, in that constant tug-of-war between security and liberty, we should come down so heavily on the side of measures that do little to stop acts of violence.

"This government is going to transform our politics so that the state has far less control over you, and you have far more control over the state," Clegg said at the outset. "This government will end the culture of spying on its citizens. It is outrageous that decent, law abiding people are regularly treated as if they have something to hide."

Those are passionate words. But they're also a challenge to U.S. officials keen on expanding intelligence gathering in public. In the wake of the failed Times Square bomb attempt, New York Mayor Michael Bloomberg has called for more video surveillance. A 3,000-camera network is going up in lower Manhattan and Midtown, and it's modeled on the so-called Ring of Steel in London, a system of hundreds of thousands of cameras that reportedly photograph the average person 300 times per day.

Bloomberg was in London last week to meet with his counterpart, Boris Johnson, who gave him an up-close look at cameras in the city's Underground stations. Bloomberg doesn't claim that the cameras actually prevent terrorism. "It's not clear that [cameras] would have helped in Times Square, other than if the perpetrator knew there were cameras, he might not have tried to come into Times Square," he told reporters. But, he argues, it couldn't hurt to have more eyes in the sky. "Nobody's going to make the world perfectly safe, but wouldn't you rather be somewhat safer?"

This isn't an effective counterterrorism strategy, and Bloomberg’s logic is based on speculation. There is no compelling evidence that a security camera has stopped someone who is determined to drive a bomb into a building or carry one onto an airplane. It's also hard to prove that broad surveillance of phone calls and emails in the United States, which shot up after the 9/11 attacks, has smothered incipient plots. Indeed, this massive collection has tended to overwhelm U.S. analysts, who now have larger haystacks to comb for needles.

For his part, Clegg appears ready to lead by example. He promised to eliminate or pull back some of the U.K.'s most controversial security policies, which collectively form the bulwark of its efforts to preempt acts of terrorism. Out is a $7.3 billion plan for a national identification card, which would be coded with biometric identification such as facial images and fingerprints, and then linked to an electronic register. Gone too is the next generation of British passports, which would also include those biometric markers. Clegg also announced new restrictions on what the government can do with private information. The authorities "will not hold your Internet and email records when there is no reason to do so," a shift that puts the onus on government to justify its spying. And Clegg committed to restrictions on a national DNA database that contains profiles of more than 5 million people, one of the largest such collections in the world, and on the use of closed circuit cameras by local authorities and businesses.

These are risky proposals for any Western leader, but especially for a country that has been attacked by religious extremists and is beset by persistent threats. Intelligence gathering is one of the most jealously guarded and legally protected authorities of a chief executive. To abandon them is to invite political ruin should a suicide bomber carry out his plans in an area unwatched by video eyes. Clegg has challenged policies that some national leaders insist provide meaningful, tangible security to the British public. Alan Johnson, the former Home Secretary, said the use of DNA records by police helped identify the perpetrators of "800 cases of rape, manslaughter and murder" each year. He blasted Clegg's speech as an act "rampant hyperbole." To cut against that opposition, as well as history's tendency to coalesce power in the hands of the state, is, as Clegg himself put it, "very radical indeed."

But lest Clegg's supporters, and those who've worked against the expansion of the surveillance state rejoice, remember that it was just a speech. The audience appeared mostly favorable to the ideas, and that was certainly no accident. Clegg's proposals still have to survive his coalition with Prime Minister David Cameron. And Clegg might also find that the weight of responsibility looks very different at the end of the campaign trail. During the 2008 U.S. presidential campaign, then Senator Barack Obama opposed a broad surveillance bill championed by George W. Bush and congressional Republicans. But as his nomination appeared secure, and his advisers—among them a former Bush official—argued that techniques such as email and phone surveillance actually helped catch terrorists, Obama reversed his position.

Still, Clegg should be applauded for challenging the conventional wisdom—much of it disproved by recent events—that more cameras, more DNA databases, and more digital monitoring actually preempts acts of terrorism.

Supporters of enhanced surveillance must offer a better argument for why, in that constant tug-of-war between security and liberty, we should come down so heavily on the side of measures that do little to stop acts of violence. Since 9/11, American and British leaders have unashamedly embraced their surveillance powers. Now, Clegg wants to change the balance, and he has proposed shedding those authorities in service of a larger goal: "Britain must not be a country where our children grow up so used to their liberty being infringed that they accept it without question."

American leaders would do well to consider this as they too deal with an increasing number of attempted attacks in this country, and the threat to liberty that our response could pose.

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Shane Harris writes about electronic surveillance, intelligence, and counterterrorism. He is a senior writer at Washingtonian magazine and the author of The Watchers: The Rise of America's Surveillance State.