Escalating music download sales have helped double the size of the U.K. singles market over the past three years, according to figures published by The Official U.K. Charts Company (OCC).

Total U.K. singles sales for the first 51 weeks in 2006 alone reached 65.1 million units, according to the chart compiler, which is a joint venture between labels body the BPI and retailers group ERA. That figure represents more than twice the quantity sold in the whole of 2004, when the number of singles sold reached 32.3 million units, and is 36% higher than the 48 million sold in 2005.

The OCC attributes the growth in singles to the explosive rise in download sales. Downloaded singles in the 51 weeks reached 51.6 million units, up from a mere 5.8 million in 2004 and nearly double the 26.6 million units consumers purchased last year.

Downloads sold represent 79% of total singles sales so far this year, with the rest accounted for by physical singles.

The news comes just before a radical overhaul of the Official Singles Chart, starting Jan. 1 (Billboard.biz Nov. 2, 2006). From that date, the sale of individual downloads, whether they are current hits, golden oldies or album tracks, will be eligible for the OCC's singles chart. Previously, to qualify for the singles chart, a physical version of the digital recording had to be released.

Existing physical formats, including vinyl, CD and DVD singles will continue to qualify. One additional rule change will see the definition of a physical EP (extended-play) or maxi-single format changed to mean four tracks with a combined playing time of 25 minutes. Previously chart-eligible EPs were restricted to three tracks with 20 minutes total playing time to prevent confusions with the album format.

"The EP has an honorable history in the charts and EPs were popular in both the 1960s and then again during the punk period," said OCC chart director Omar Kasatiya in a statement. "We hope this rule change will lead to a revival of the EP and a boost to sales of singles through record stores."