It appears that the Bristol branch of Indymedia the independent / alternative news network, has fallen foul of heavy handed Police authorities in search of an elusive, and probably non-existant IP address of an otherwise anonymous author of a posting on their news bulletin board / forum - no different in principle from a web blog or discussion forum with open comments.
It appears that the British Transport Police have seized an Indymedia server machine from the home of a volunteer, who has also been arrested, allegedly due to a "news" article which implies that the anonymous author was involved in some criminal damage to some railway freight traffic. Presumably they were after an IP address of the "anonymous" poster, which, if the server was set up as Indymedia usually claim, would not have been keeping a log file of this information.
This should be a case for a Regulation of Investigatory Powers request to the server's Internet Service Provider, and should not have lead to the arrest of a member of an alternative media volunteer/journalist.
Indymedia were targeted last October by a international muli-lateral jurisdictional nightmare , which ended up with two of their servers hosted by Rackspace, near Heathrow being seized on the orders of the FBI, acting on still mysterious Italian or Swiss authorities, without consulting the local United Kingdom police authorities, who had legal jurisdiction.