A revolution in music downloads has been hailed as a victory for music lovers - and the biggest challenge yet to Apple and its iTunes store. A new service from internet firm 7digital.com means tracks will be available from the big four record companies without a digital lock.

In the past, Apple and other official download sites have sold music with a digital lock which meant it could only be played on a single device and could not be copied. The lock - known as Digital Rights Management (DRM) - was always a great frustration to music lovers who resented the limits imposed on how they listened to their favourite artists.

Now, in a major victory for consumer power, 7digital will offer music in the MP3 format which can be downloaded to iPods, other MP3 players, mobile phones and Blackberries.

In the past, three of the big four record labels - EMI, Universal and Warner - had agreed to remove DRM from their downloads. Now the final big name, Sony BMG, whose artists include Bob Dylan, Metallica, Kings of Leon and Michael Jackson, has agreed to follow suit. Some four million tracks are available for the 7Digital service featuring artists ranging from Amy Winehouse to The Cure and jazz legends like Miles Davis.

New music services without the digital lock are expected to be announced shortly by Amazon and MySpace, creating yet more competition for Apple’s iTunes.

The company, which said it is expanding services in Europe and north America, has announced a partner programme to allow third parties to sell music via its service. Tracks on the service generally cost 79p each, while the cost of an album is typically £7.99 source