A High Court judge has ruled that BT must block access to the Newzbin website which provides links to pirated movies.
Newzbin is a members-only site which aggregates a large amount of the illegally copied material found on Usenet discussion forums.
The landmark case is the first time that an ISP has been ordered to block access to such a site.
It paves the way for other websites to be censored in the future.
In his ruling, Mr Justice Arnold stated: “In my judgment it follows that BT has actual knowledge of other persons using its service to infringe copyright: it knows that the users and operators of Newzbin 2 infringe copyright on a large scale, and in particular infringe the copyrights of the studios in large numbers of their films and television programmes.”
He continued: “It knows that the users of Newzbin 2 include BT subscribers, and it knows those users use its service to receive infringing copies of copyright works made available to them by Newzbin 2.”
BT and the Motion Picture Association (MPA), which brought the case, will be back in court in October to work out how the blocking will work. BT said it will not appeal the ruling.
The MPA which represents a number of movie studios including Warner, Disney and Fox, launched the legal action as a last-ditch attempt to close down Newzbin 2.
The MPA signalled its intention to pursue other ISPs.
Link sites such as Newzbin 2 are gaining popularity as those determined to get their hands on free content move away from traditional peer-to-peer downloading methods.
A previous court case had ruled that Newzbin 2′s predecessor must stop linking to free content but a new version of the site was set up outside of the UK’s jurisdiction in Sweden.
Justice Arnold ruled that BT must use its blocking technology CleanFeed – which is currently used to prevent access to websites featuring child sexual abuse – to block Newzbin 2.
The Internet Service Providers’ Association has been a fierce critic of web blocking. It said that using blocking technology designed to protect the public from images of child abuse, was inappropriate.
Digital rights organisation the Open Rights Group said the result could set a “dangerous” precedent.
“Website blocking is pointless and dangerous. These judgements won’t work to stop infringement or boost creative industries.
“And there are serious risks of legitimate content being blocked and service slowdown. If the goal is boosting creators’ ability to make money from their work then we need to abandon these technologically naive measures, focus on genuine market reforms, and satisfy unmet consumer demand,” said ORG campaigner Peter Bradwell.