The overall decline came despite continued growth in digital album sales, which rose 17.3 percent year-on-year.

The singles market continued to expand, with sales reaching 93.6 million in the first six months of the year, a rise of 6.3 percent from the first half of 2011. Digital downloads accounted for 100 percent of sales of the top 10 singles of 2012 so far.

"We've had another solid quarter of digital growth in sales volumes - both in albums and on singles, where the top 10 were exclusively sold as digital downloads," said BPI chief executive Geoff Taylor in a statement.

"Album unit sales are down quite significantly year-on-year, but it's important to remember that these unit sales figures do not take into account the growing importance of music streaming and subscription services."

Adele's "21" was the best selling artist album of the year so far in 2012, mirroring its performance as the biggest seller from the first half of 2011 a year ago.

"Our Version Of Events" by Emeli Sande is the second-biggest artist seller of 2012, with Lana Del Rey's "Born To Die" third.

Britain's biggest-selling single of 2012 so far is "Somebody That I Used To Know" by Gotye featuring Kimbra, which has sold more than a million copies. It is followed by "Call Me Maybe" by Carly Rae Jepsen and "Titanium" by David Guetta featuring Sia.

"The second half of 2012 is looking very promising for music fans, with big releases anticipated from The Killers, Plan B, Joss Stone, Mumford & Sons, Robbie Williams, Muse, David Guetta, Van Morrison, Pet Shop Boys, Dido, One Direction and The Vaccines," Taylor added.

(Reporting by Mike Collett-White, editing by Paul Casciato)

• A Permanent Economic Emergency