The EU Security Commissioner has warned technology companies that they will face regulation if they don’t remove extremist content more quickly.
Sir Julian King told Sky News: "I hope that we're going to be able to make progress, we are taking down tens of thousands of such material but there are hundreds of thousands out there, if not more.
"It gets taken down quite quickly but all the studies show that it's in the first couple of hours where it has its most effect.
"So what we've said is that we want to see those companies using all of their technical expertise – automatic, automated means- to spot and take down stuff very quickly if not stopping it being uploaded in the first place.
"In the Commission we've said we're going to review the situation early next year and we reserve the right to look at legislation and regulation if we are not making the progress we need to make."
Sir Julian was speaking at a meeting of EU representatives at the UK National Cybersecurity Centre, part of GCHQ.
He told Sky News that even under a "no deal" Brexit, cybersecurity cooperation would continue.
"Whatever else happens in those discussions, both sides, both the EU 27 and the UK government have said very clearly that co-operation on security matters should be unconditional, that is fighting terrorism, fighting cyber threats and serious and organised crime because these are clearly shared threats, they are best met by working together.
"It doesn't matter how good you are at dealing with these threats you are still stronger if you do it with partners and I think that shared objective is clearly acknowledged now by all those involved in this process."
Ciaran Martin, the chief executive of the NCSC made the same commitment.
"Our support in cybersecurity to European partners is unconditional," he said.
Mr Martin highlighted the threat to democratic processes posed in the digital realm, but said that, despite successful attacks on the US and Germany, the integrity of recent UK elections and referendums had been preserved.
"We've yet to see any successful outside interference in any UK election," he told Sky News.
"Of course cyber intrusions can take place for a variety of reasons and you can't always tell – if a hostile state has intruded into a particular network – what the purpose of that intrusion was.
"So I can never categorically say that there hasn't been an attempt on UK electoral process. What I can say is there hasn't been a successful attempt to date.
"Clearly, given what's happening internationally, it's a concern and one that on the top of our priority list."
Mr Martin identified Russia as the biggest worry for threats to electoral systems, but also highlighted North Korea and Iran, as well as China.
"The Chinese threat is something that varies in terms of sophistication and intensity. So we've seen over many years a Chinese espionage campaign against the United Kingdom.
"There's been an agreement since September 2015 against commercial espionage. And what we're now seeing is a different type of threat from China in cyberspace.
"What is happening is that this sort of high-level prolific attacks are not as visible as they were in the past. So it's the more sophisticated, state level attack that we are concerned about."