More jihadist propaganda is viewed online in the UK than any other country in Europe, according to major new report.
The think tank Policy Exchange said only Turkey, the US, Saudi Arabia and Iraq registered more clicks for jihadist content online, such as execution videos and bomb-making instructions.
Experts say IS - also known as ISIS or Daesh - produces around 100 pieces of new content in an average week, and that its decline online has been "significantly overstated".
The 131-page assessment reveals that tens of thousands of users access jihadist material online from all over the globe.
Concerns over the availability of terrorist material on the internet have intensified after the UK was targeted by its fifth terror attack of the year last week.
The report details how:
- In an average week IS produces over one hundred new articles, videos and newspapers;
- They are disseminated across a "vast ecosystem" of platforms, file sharing services, websites and social media;
- IS now uses encrypted messaging service Telegram as the core communication platform for talking to sympathisers;
- But jihadists have not abandoned other platforms, with content also regularly accessed via Facebook, Google and Twitter;
- Three in four people (74%) want big internet companies to be more proactive in locating and deleting extremist content, according to a poll.
Lead author Dr Martyn Frampton said governments and security services have been playing a "fruitless game of 'whack-a-mole"' which is focused on removing individual pieces of content.
He warned: "The evidence suggests that we are not winning the war against online extremism.
"If the internet companies won't do what their customers want and take more responsibility for removing this content, then government must take action through additional regulation and legislation."
This week Prime Minister Theresa May and French president Emmanuel Macron will hold talks to discuss possible new measures to tackle the problem.
It emerged earlier this year that Britain and France are looking at plans that could see technology firms face fines if their efforts are not up to scratch.
Home Secretary Amber Rudd warned the internet must not be a "safe space" for terrorists and criminals.
- What are the internet giants doing to help?
Facebook, Microsoft, Twitter and YouTube have set up the Global Internet Forum to Counter Terrorism to spearhead efforts to clamp down on extremist content.
Twitter says terrorist content has no place on the platform.
Figures published by the microblogging site show 636,248 accounts were suspended in total between August 2015 and December 2016 for the promotion of terrorism.
Google said violent extremism was a "complex problem" and that it is "making significant progress" in tackling the issue.
Facebook said it is committed to fighting online extremism and works "aggressively" to remove terrorist content as soon as it becomes aware of it.