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.”