Apple's iTunes Music Store dominates the UK downloads market with 80 per cent of transactions, according to the Official UK Charts Company.

Apple claims to have the largest music catalogue in the UK with 1.7 million tracks for download, just 100,000 more than Napster.

Napster recently announced that it has 750,000 registered users, 80 per cent of whom are over 25 years old. Over the past 15 months its customers have downloaded or streamed 55 million tracks from its 1.6 million track catalogue.

However, the iTunes market share looks almost guaranteed to decline now that HMV and Virgin have launched services in a market that also contains Tesco and Woolworths. The independent firm Wippit is also a competitor.

Apple is expected to launch either an iTunes mobile phone in conjunction with Motorola or a video iPod today.