Pharrell Williams' hit Happy has brought further joy to his music bosses by pulling off a rare sales feat.

The track has become only the fourth single to be declared triple platinum in the past 20 years, meaning it has achieved 1.8 million sales.

Happy, which featured in the soundtrack to the movie Despicable Me 2, topped the singles chart in December and it has not left the top 20 this year.

Music industry body the BPI incorporated data for online streaming into its sales awards earlier this month - at the same time the figures were incorporated into the singles chart - with 100 plays on legitimate services judged to be the equivalent of one sale.

Happy has notched up more than 25 million streams, the equivalent of 250,000 sales which has taken it past the 1.8 million barrier in addition to physical sales.

Gennaro Castaldo of the BPI said: "Every now and then a song comes along that captures the public mood and becomes a feelgood anthem for a generation.

"Happy is not only one of the most successful multi-platinum recordings of all time, it has taken on near-iconic status and has helped to propel Pharrell to global superstardom."

For singles to go platinum they have to have notched up 600,000 sales, while for gold the figure is 400,000 and for silver it is 200,000.

The only other singles to sell 1.8 million are Will Young's Anything Is Possible/Evergreen, Aqua's Barbie Girl and the biggest selling UK single of all times, Sir Elton John's Candle In The Wind 1997/Something About The Way You Look Tonight.

Colin Barlow, the managing director of Pharrell's music label RCA, said: "Pharrell is one of the most innovative producers, writers and performers to emerge from the world of music in the last 20 years."