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The U.K.’s big internet service providers, including BT, Talk Talk, Virgin Media and Sky, have agreed to filter out terrorist and extremist material at the government’s behest, in order to stop people seeing things that may make them sympathetic towards terrorists.

The move will also see providers host a public reporting button for terrorist material. This is likely to be similar to what is already done with websites that may host child pornography – people can report content to the Internet Watch Foundation (IWF), an organization that maintains a blacklist, to which that site could then be added.

In the case of extremist material, though, it appears that the reports would go through to the Counter Terrorism Internet Referral Unit (CTIRU), which is based in London’s Metropolitan Police and has already been very active in identifying extremist material and having it taken down. CTIRU told me in a statement: “The unit works with UK based companies that are hosting such material. However the unit has also established good working relationships with companies overseas in order to make the internet a more hostile place for terrorists.”

Government sources also told me that Facebook, Google, Yahoo and Twitter have agreed to “raise their standards and improve their capacity to deal with this material.”

Jim Killock, executive director for the Open Rights Group, said in a statement: “We need transparency whenever content is blocked for political reasons. Companies have a duty to protect free speech, and should be extremely wary of taking responsibility for deciding whose views are acceptable. It is better left to the courts.”

The decision comes a year after the British government said it would force ISPs to block “extremist” websites. On Friday Prime Minister David Cameron, who is visiting Australia, told that country’s parliament:

A new and pressing challenge is getting extremist material taken down from the internet. There is a role for government in that. We must not allow the internet to be an ungoverned space. But there is a role for companies too. In the UK, we are pushing them to do more, including strengthening filters, improving reporting mechanisms and being more proactive in taking down this harmful material. We are making progress, but there is further to go. This is their social responsibility, and we expect them to live up to it.

The Australian government will also get its ISPs to filter out extremist material, sources told me, adding that the aim is “to prevent children and young people coming across radicalizing material.”

I’m not sure which internet Cameron is talking about, as the one I’m familiar is anything but “ungoverned”. Indeed, it’s frequently subject to multiple overlapping jurisdictions – for example, U.S. copyright laws affect what the rest of the world can see through services such as YouTube and its Patriot Act claims dominion over data stored all over the world, the U.K.’s DRIP Act mandates that foreign web firms retain data on their users, and some people even want Europe’s privacy laws to affect what everyone in the world can find on major search engines.

Anyhow, there aren’t many details of the new policy floating around yet — the ISPs are at the time of writing still preparing their statements, and the ISP Association refused to comment – but I am extremely worried about the idea of CTIRU maintaining a blacklist for what can and can’t be viewed online.

Even the IWF has shown itself on occasion to be worryingly unaccountable — an obscure anti-terrorism unit is hardly likely to be better. And, if ISPs maintain their own censorship systems, their anti-pornography filters’ propensity for false positives is also less than reassuring.

When new GCHQ spy chief Robert Hannigan said 10 days ago that the internet was a haven for terrorist recruitment, I suspected that this was a prelude to a new wave of censorship. I’d rather that I hadn’t been right about that. Now the U.K. can sit less-than-proudly alongside Russia as a country that won’t let its citizens see material that might make them think bad things.

This article was updated at 3.45am PT to include Killock’s statement and clarify what is already done with child pornography reporting.