LONDON — British police and security services already have some of the most powerful surveillance laws in the world, with weak judicial oversight and little criticism on privacy issues from a public that generally trusts its government and Civil Service.
Surveillance cameras are everywhere, especially in cities, and there are relatively few restrictions on the mass collection of telephone and internet data by the government.
All of which raises the uncomfortable question of what more can be done to prevent the kind of terrorist attack that killed seven people in central London over the weekend. After three terrorist attacks in 73 days, Britain is engaged in a new debate about balancing civil liberties and security, just days before voting in parliamentary elections on Thursday.
It is a familiar dilemma in the United States, where President Trump’s effort to restrict immigration from predominantly Muslim countries is blocked by courts, as well as for governments across Europe, particularly in France, which has suffered even deadlier terrorist attacks than Britain in recent years.
France has repeatedly extended a state of emergency imposed after the November 2015 attacks in Paris. Despite the huge armed presence in public spaces and new detention and surveillance powers, the impact has been limited, and, if anything, it may be further alienating already marginalized communities.
Prime Minister Theresa May talked tough as she addressed the nation on Sunday, the morning after the attack at London Bridge and Borough Market. “There is, to be frank, far too much tolerance of extremism in our country,” she said.
Her comments were criticized as political and brought concerns about whether, if re-elected, her antiterrorism plans could be effective and also protect civil liberties. In her remarks, she announced a review of counterterrorism policy, harsher sentences for terrorism offenses, and an effort to crack down on “safe spaces” online and in self-segregated Muslim communities that can harbor extremism.
“It will only be defeated when we turn people’s minds away from this violence,” she said, and make young people “understand that our values, pluralistic British values, are superior to anything offered by the preachers and supporters of hate.”
That was a departure for the British government, said Alan Mendoza, executive director of the Henry Jackson Society, a politically conservative research organization in London that focuses on democracy and anti-extremism.
“For a long time, this government didn’t really look at the ideology of radical Islam, but law and order,” he said.
Mrs. May recognized on Sunday, he added, “that ideology is the central point, and that the ideological challenge will be tougher, to talk to communities and push them to resolve the ideological fight within themselves.”
François Heisbourg, a security expert and adviser to the new French president, Emmanuel Macron, agreed. For the last decade, he said, the British have promoted a policy of getting Muslim communities to cooperate with security forces, “which is pretty much the opposite of the French approach.”
Mrs. May is acknowledging that “the communities are not so good at policing themselves,” Mr. Heisbourg said.
CreditAndrew Testa for The New York Times
“You need more grass-roots intelligence, not community intelligence,” he said, with less delicacy about community sensitivities and more willingness on the part of the British to use the vast powers they already have under the law.
In a time of growing anxiety over terrorism, it is a bargain that Europeans may be more inclined to accept. There were, for instance, no protests when France’s new government suggested last month that it would seek a sixth extension for the state emergency the country has been living under for a year and a half.
But it is not clear that tougher surveillance and policing measures alone are the solution. Mrs. May promises more help for stretched counterterrorism police and intelligence agencies.
But Mrs. May was selling old rope, said Peter R. Neumann, a professor of security studies at King’s College London and director of the International Center for the Study of Radicalization. The statements amount to a recycling of previous efforts to toughen antiterrorism laws, he added, and of the Conservative Party’s criticism of the powers of internet and social media companies to resist targeted government surveillance of suspects. That theme is also prominent in the party’s election platform.
In fact, Mr. Neumann said, technology companies are much more responsive now to government requests to shut down accounts or videos expressing extremist views than they were three years ago. But that has pushed extremists to use encrypted channels of communication, like Telegram, he said.
“You can’t eradicate the internet,” he said. “These people have not gone away but gone to a different platform, one much more difficult for intelligence agencies to monitor.”
Mrs. May and her predecessor, David Cameron, regularly pushed big technology companies to allow a “back door” for intelligence agencies into encrypted communications. While the companies have quietly been much more helpful on security cases, they have refused those “back door” requests, although intelligence agencies are working separately to create them.
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On Sunday, Mrs. May’s successor as home secretary, Amber Rudd, said that technology companies could do “so much more” to restrict extremism online. “It is not good enough to say, ‘Do no harm.’ We have to get them to actively work with us to stop their platforms being used to radicalize people.”
She said that more needed to be done to take down extremist materials, but she also said that social media giants should limit end-to-end encryption, which many extremist groups use to plot attacks.
These are familiar Tory themes. Mrs. May herself has called for democratic governments to demand greater controls over how services like WhatsApp and FaceTime could be used by attackers to spread extremist messages online, as well as how extremists could use social media to promote their views to a global digital audience.
These demands have raised concerns from some of Silicon Valley’s largest companies, as well as from online-privacy campaigners, which claim that the new powers would infringe on people’s liberties.
After last month’s terrorist attack in Manchester, for instance, Mrs. May and other British lawmakers said they would revisit plans to force tech companies to open their encrypted message services to the country’s intelligence agencies, allowing them to monitor messages sent by people suspected of planning attacks.
The step comes less than a year after the British government passed some of the most far-reaching legislation in the world, giving law enforcement agencies widespread powers to monitor both internet and phone traffic. Britain currently has access to the metadata of online communications without a warrant, but not to the content of individual messages.
In recent years, tech companies have repeatedly said they are willing to work with law enforcement to crack down on extremists using their services, but they have added that weakening encryption could also allow for the illegal collection of personal information by domestic or foreign intelligence services, among others.
“In terms of surveillance power, Britain is already better equipped than any other European country,” said Mr. Neumann of King’s College London. “There is no real judicial oversight: Cabinet ministers sign off on warrants, so the executive signs off on itself.”
Unlike in the United States, the British Parliament’s intelligence oversight committee is weak and has very little subpoena power.
“The British have no trouble listening in to anyone’s phone or going into anyone’s house,” he said. “But the government uses those powers very carefully, which shows how the unspoken consensus here works,” he added, noting that the country has no written Constitution.
In countries with written Constitutions, like Germany and the United States, “you can define extremism as those opposed to the precepts of the Constitution,” Mr. Neumann said. “May talked of ‘British values’ as the antithesis to extremism, but it’s hard to articulate what extremism means and enforce it legally” — let alone decide what British values actually mean.”
“You can say that means being friendly, moderate and polite,” he continued. “But you can’t legislate politeness.”
He pointed to the case of Anjem Choudary, a lawyer who managed to avoid breaking the law while spending nearly two decades preaching jihadist views. He was convicted in 2016, only when film emerged of him pledging allegiance to the Islamic State, and he was sentenced to five years and six months in prison.
There are unconfirmed reports that at least one of the London assailants was a Muslim who had been influenced by Mr. Choudary.
“Choudary was for years the single person most responsible for Islamist recruiting and propaganda, but he wasn’t charged until 2015, when May had been home secretary for five years,” Mr. Neumann said.
“He was a real life radical preacher who recruited people face to face,” he said, “and much more important for jihad in Britain than Twitter or Facebook.”