The investigation was conducted by Avon and Somerset Police in conjunction with film industry trade body the Federation Against Copyright Theft (FACT).
"A 50 year old man was arrested on July 27th on suspicion of breaching the Copyright and Patents Act," said a spokeswoman for Avon and Somerset Police. "He has been released on police bail pending further enquiries. The operation was run jointly with FACT."
An account of the arrest posted at Filesoup which purports to be from the man, who is known only as Geeker, said that he was held in a police station for seven hours and that 33 items were taken from his house.
According to file-sharing news site Torrentfreak.com, Filesoup is one of the oldest sites of its kind. It claims that the site has never hosted any copyrighted content, but "links to metadata which links to material hosted elsewhere."
The account posted at Filesoup claims that the search warrant was issued under Section 109 of the Copyright, Designs and Patents Act of 1988. That provision in the Act allows a search of premises when there are reasonable grounds for believing that certain offences have been or are about to be committed.
These offences include distributing an infringing work and "communicating the work to the public," either in the course of a business or "otherwise than in the course of a business to such an extent as to affect prejudicially the owner of the copyright".
Geeker's posting says that when he arrived at the police station his "booking-in charge" was entered as "Suspicion of downloading copyrighted movies".
His account says that documentation given to him about the seized items said that he should apply for their examination or return to Neil Gardner, a senior investigator with FACT at a FACT address.
A FACT spokesman declined to confirm or deny whether it had the material in its possession but said that it was not uncommon for police to use outside organisations to assess or analyse evidence.
The police spokeswoman would not say whether it or FACT had physical custody of the material but said that as long as the police have lawful possession of the material it can be given to external bodies for examination.
Evidence in a criminal trial was handed over by police to FACT in a recent case involving company Scopelight in which individuals were accused of web-related piracy. They were never charged.
FACT refused to return the evidence to police or Scopelight once the police said there was not enough evidence for a prosecution. The High Court said in May that retention of the material was against the law, and that the police were not permitted to keep material seized for a criminal prosecution on behalf of a private organisation.
The police and FACT have appealed the ruling and a Court of Appeal hearing is expected in September.
A third internet piracy case was pursued by the police and FACT in 2007 when a Gloucestershire man was arrested for allegedly running a website, TV-links.co.uk, that linked to pirated television content. According to the Guardian newspaper, no charges were brought but the site was shut down.