The Home Office have now replied to my Parliamentary Question on Indymedia and a similar one from Jeremy Corbyn MP as follows:
Mr. Allan: To ask the Secretary of State for the Home Department which UK law enforcement agencies were involved in the seizure of computer disks containing material published by Indymedia from the London offices of Rackspace. 
Caroline Flint [holding answer 18 October 2004]: I can confirm that no UK law enforcement agencies were involved in the matter referred to in the question posed by the hon. Member for Sheffield, Hallam.
Jeremy Corbyn: To ask the Secretary of State for the Home Department under what powers, and acting under what information, officials of his Department seized web services belonging to Indymedia; and if he will make a statement. 
Caroline Flint: I can confirm that no UK law enforcement agencies were involved in the matter referred to in the question posed by my hon. Friend. In the circumstances I do not therefore believe that it is necessary for me to make a statement.
I suspected that this would be the answer though the Home Office have obviously spent a few days checking with all agencies to ensure that they can accurately deny any involvement. What this means is that any action will have to be directed against Rackspace rather than the UK authorities. Indymedia may have both civil and criminal complaints to bring against them if they have acted illegally. The nature of any such action will depend on their legal advice. I will do what I can to press the UK authorities to assist where necessary.