The total number of records sold to date in 2012 is 43.6m, down from 50.5m in 2011, the BPI reports.
However, sales of digital albums have increased by 17.3% this year, with digital downloads accounting for 34.7% of all albums sold in the past three months.
Sales of singles totalled 93.6m for the first half of 2012, up 6.3% year-on-year compared with 2011's 88m. Digital sales accounted for 100% of sales of the top ten singles of 2012 so far.
BPI Chief Executive Geoff Taylor said: "We've had another solid quarter of digital growth in sales volumes - both in albums and on singles, where the top ten were exclusively sold as digital downloads.
"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.
"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."
'Somebody That I Used to Know' by Gotye featuring Kimbra is the UK's biggest-selling single of 2012 so far, having shifted over a million copies. 'Call Me Maybe' by Carly Rae Jepsen is in second place, followed by David Guetta and Sia's 'Titanium'.
It was revealed yesterday (July 2) that Adele's 21 is the biggest-selling album of 2012 so far, despite being released in January 2011.
Watch Gotye's video for 'Somebody That I Used to Know' featuring Kimbra below: