Developers of peer-to-peer (P2P) software have formed a trade association and drawn up a code of conduct for users of file-swapping sites, in the hope of helping to mollify the US music industry.

The association, P2P United, is made up of six P2P companies, including Grokster and Streamcast - but not Sharman Networks, developer of Kazaa.

It intends to lobby the US Congress to introduce compulsory licensing, a system similar to the fees that radio stations pay for music.

If successful the recording industry, which has so far refused to open up its catalogues of music to P2P sites, would be forced to make its music available, giving P2P providers legitimacy.

The code of conduct, according to P2P United, will help encourage responsible behaviour among the millions of users who copy music and other material from each other's hard drives.

The code warns users: "The use of the software for illegal activities, including particularly infringement of intellectual property laws, is strictly forbidden and may subject the user to civil and/or criminal penalties."

But sticking to the code is up to individual users, and the group does not promise to police sites for infringements.

The Recording Industry Association of America (RIAA) said it was refreshing that P2P United had acknowledged that its members should more actively educate users about the consequences of rampant illegal file sharing.

"But, let's face it, they need to do a whole lot more before they can claim to be legitimate businesses," it added.

The RIAA recently launched 261 lawsuits against P2P users. Of these, 62 are said to have been settled out of court.

According to market analyst Informa Media, the value of songs downloaded from P2P networks such as Grokster and Kazaa will rise to $6.3bn by 2008, compared to $3.2bn this year.

Simon Dyson, the report's author, said: "We think the P2P problem is going to only get worse. In 2008, broadband will be prevalent around the world."