The British Phonographic Industry (BPI) is threatening to take legal action against a small hardcore of file sharers "offering hundreds and often thousands of files over the internet", out of the seven million people in the UK it claims use illegal music download sites.

The UK record industry association has said it will put illegal file sharers of music "on notice" that if they continue their activities they will face court action.

Research also published today by the BPI reports that retail spending on music is down by almost a third on albums (32 per cent) and almost 60 per cent on singles (59 per cent).

Only 600,000 users stick to legal sites, the BPI claimed.

"These figures are truly disturbing. No-one can now question the need for us to take action," said Peter Jamieson, chairman of the BPI, in a statement.

Initially, the BPI is launching an instant messaging campaign warning uploaders that they face court action if they do not disable file sharing software on their computers, a similar tactic to that deployed by the RIAA in the run up to its first set of lawsuits.

The message states: "Warning: The file sharing network you are connected to indicates that you are offering music to others from your computer.

"Doing this without permission from the copyright owner is illegal."

"There is no excuse whatsoever for people taking music without permission," said Jamieson.

"There are literally hundreds of thousands of tracks available on legal internet music services in the UK."

File sharing contravenes Sections 16 and 20 of the The Copyright, Design and Patents Act 1988, according to the BPI.