The International Federation of the Phonographic Industry (IFPI) is threatening internet service providers with legal action if they refuse to stamp on customers illegally sharing files.

The IFPI said in its annual report into the music industry that a doubling in digital music sales last year was not enough to offset the fall in CD sales, which it partly attributes to piracy.

"As an industry we are enforcing our rights decisively in the fight against piracy and this will continue. However, we should not be doing this job alone," said IFPI chairman John Kennedy.

"With cooperation from ISPs we could make huge strides in tackling internet piracy globally.

"It is very unfortunate that it seems to need pressure from governments or even action in the courts to achieve this, but as an industry we are determined to see this campaign through to the end."

The organisation said that there was evidence that the current policy of taking legal action against file sharers is working.

The IFPI cited a Jupiter Research document showing that, while broadband penetration in Europe doubled to 40 per cent between 2004 and 2006, the proportion of users regularly file-sharing fell from 18 per cent to 14 per cent.

A spokesman for the Internet Services Providers Association said: "ISPs are commercial entities, not law enforcement organisations, just as the IFPI is a trade body, not the law.

"ISPs are not hosting this material, they are just conduits for it and cannot monitor content. It is against data protection laws to do so."