LONDON — Retro soul music act Gnarls Barkley has stormed to the top of the U.K. music charts on the strength of downloads alone, marking the first time a track has been number one in the U.K. before the release of the physical single.

Boasting over 31,000 legal downloads, Barkley’s tune “Crazy” shot to the top as the result of a rule change recently instituted that allows download sales to count as long as a CD is released the following week. The physical CD hits shops April 3.

“This not only represents a watershed in how the charts are compiled, but shows that legal downloads have come of age,” said Gennaro Castaldo, spokesman for retailer HMV.

The growing significance of download driven buzz was highlighted by the emergence of breakthrough Brit rock act “The Ar-tic Monkeys,” whose recent meteoric rise was powered by popularity on the Internet.

“Crazy” received a big boost when it was selected for advertisements for DJ Zane Lowe’s popular BBC Radio 1 show.

Gnarls Barkley is the pseudonym of U.S. rap producer Danger Mouse and singer Cee-Lo Green.