Cassandra's curse was that she could see the coming future, but couldn't convince others of her credibility. A pessimist's is that even if they convince the world, it's not going to be a good day when that bleak forecast is proved correct. I'd already figured that out. But I didn't expect that the very public curtailment of Britain's internet freedoms would be signalled by the non-appearance of a sleazy and exploitative Kraut-rock album sleeve I last saw in my sixth-form common room some 30 years ago.

It's partly the fact that the Scorpions' Virgin Killer has been around all that time without the hint of a prosecution, and partly the cackhanded way the Internet Watch Foundation has gone about justifying its censorship, not to mention the side-effect of wiping out British editing capability on Wikipedia, that seems to have created bemusement on the web, rather than anger. The linked image is held on Amazon in the US for instance – but the IWF hasn't sought to block Amazon. I compiled a report for Index on Censorship on banned music 10 years ago – there must be a thousand album covers that have upset the censors in their day. The IWF could have picked Houses of the Holy, Nevermind, or Blind Faith.

Instead, they've used their peculiar position as an unaccountable body to impose this censorship on an obscure metal album and some 95% of British web users. The IWF, a notionally independent charity, in fact acts as a quasi-governmental clearing house for every nutjob with a bee in his bonnet about other people's surfing habits. Without any legal authority or legislative backing, this secretive group prepares a list of prohibited IP addresses, which it forwards to ISPs, and to the British government. We're not privy to any information regarding the British government's own additions to the list – they could add anything. No one outside a tiny department in the Home Office would know. Thanks to government bully-boy tactics, all British ISPs now promise to implement the IWF's blacked list – again, regardless of the legality or veracity of the list.

It isn't clear why some ISPs have failed to block the Wikipedia pages – some censorship has clearly been propagated automatically; but perhaps some ISPs are looking across the Atlantic for guidance, where a related FBI investigation concluded that the album artwork broke no US laws. Unfortunately the ISP's aren't talking. But what we can tell from the technical details is that the architecture for censorship of the internet in Britain is alarmingly sophisticated.

ISPs were able to block the pages in a trice – all their traffic flows through devices that monitor for prohibited destinations. If banned requests are intercepted, the user request goes no further and a "404 page not found" error is returned, or simply a blank page. The hardware infrastructure for this kind of national processing doesn't come cheap, it isn't easy to set up and it must have taken some time to implement. This is an expensive, powerful, integrated censorship that leads the world. It didn't happen by accident.

Nor did it happen in secret – hence some pessimistic satisfaction at my predictions coming true. I've written of the far-reaching impact of Cleanfeed and the gentlemen's agreements between government and ISPs – all without any democratic control. "Paranoid" is one of the most common insults in the comments below my articles. I hope no one is muttering about paranoia now.