Wrapping up the last of the United Kingdom's notorious copyright infringement "pay up" letter cases, a UK patent and copyright judge has had a major revelation. Just because some lawyer cites an Internet Protocol (IP) address where illegal file sharing may have taken place, that doesn't mean that the subscriber living there necessarily did the dirty deed. Or is responsible for others who may have done it.

"What if the defendant authorises another to use their Internet connection in general and, unknown to them, the authorised user uses P2P software and infringes copyright?" asked His Honour Judge Birss QC last Tuesday.

What indeed? The question comes in the case of MediaCAT Limited versus 27 defendants accused of sharing online porn. The copyright holding group is represented by lawyer Andrew Crossley of ACS:Law. He wants around £500 apiece from the accused, even though most of his cases show little evidence of individual guilt.

But what makes the England and Wales Patent County Court ruling particularly interesting is the jurist's obvious skepticism about what has become the central dogma behind these suits - that a torrent share associated with a specific IP address is grounds for legal action against a specific human being. The lawyers argued that, even if the Internet subscriber hadn't done the deed, he or she had presumably let someone else use their network, and so were therefore responsible for this "authorized" use.

"Does the act of authorising use of an Internet connection turn the person doing the authorising into a person authorising the infringement within s16(2)?" Birss asked. "I am not aware of a case which decides that question either."

All this may seem rather obvious, but these are key principles that are only now finding their way in major judicial opinions. The revelations could have some serious implications for the UK's Digital Economy Act, too. That law requires ISPs to forward P2P warning letters from copyright holders, and it opens the door to throttling and Internet disconnection for repeat infringement.

Central to the Act's enforcement logic is the idea that the activities associated with an IP address demonstrate the culpability of the address owner. Such is the official fealty to this precept that last year one UK government defender of the Act mistakenly called IP your "Intellectual Property" address.

But Judge Birss has clearly discovered that the digital emperor of this assumption has few if any garments. "Proof that a person owns a photocopier does not prove they have committed acts of copyright infringement."