Britain will not be safe from terrorism until Islamic State's online presence is wiped out, a senior security official has warned.
Patrick McGuinness, a deputy national security adviser at the UK's Cabinet Office, the internet is now the "frontline" and called on tech firms to go further in tackling the problem.
"The speed with which people are brought to violence is almost too fast to catch without the most extraordinary, intrusive surveillance techniques which are not going to be sustainable or acceptable in a Western democracy."
Speaking at a conference in London, McGuinness said major firms are "increasingly cooperative" and had shown a "real sense of willingness and collaboration".
"When spam looked like it was going to overcome our inboxes, miraculously they found a way of filtering it away."
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Britain's most senior counter-terrorism officer Assistant Commissioner Mark Rowley flagged up the challenge posed by web content and encrypted communications.
"We are seeing vulnerable people in our communities being radicalised and a large part of that radicalisation comes from that online propaganda footprint.
"We are seeing untraceable attack planning being done between conspirators. We are seeing the ability to procure bomb-making instructions online."
Concerns over online material have intensified after Britain was hit by five attacks this year, while another seven plots have been foiled.
Security services and police are running hundreds of live operations involving around 3000 individuals, while there is also a pool of more than 20,000 people looked at as part of previous terror investigations.
The head of MI5 has said technology companies have an "ethical responsibility" to help confront the unprecedented threat, while Britain and France are exploring plans that could see platforms face fines if their efforts are not up to scratch.
