Duffy and Alexandra Burke were the UK's top-selling musicians of the year, according to official sales figures.
X Factor winner Burke sold 888,000 copies of her version of Hallelujah in the last two weeks of the year to take the year's biggest-selling single.
Duffy's debut album Rockferry held off a late challenge from Take That to come top of the year-end chart, with 1.685 million copies sold.
Kings of Leon, Leona Lewis and Coldplay all sold over a million albums in 2008.
TOP SINGLES OF 2008
Duffy's Mercy sold 536,000 copies, the only other single to sell over half a million.
Katy Perry's I Kissed A Girl was the fourth biggest-seller, followed by Nickelback's Rockstar.
Other top-selling singles included Estelle and Kanye West's American Boy, Kings of Leon's Sex on Fire, Basshunter's Now You're Gone and Madonna and Justin Timberlake's collaboration 4 Minutes.
Sam Sparro's Black & Gold rounded off the year's top 10 singles.
Rihanna, Killers, Girls Aloud, Pink and Scouting For Girls all feature in the top 10 albums of 2008.
TOP ALBUMS OF 2008
The figures include both downloads and physical copies such as compact discs.
OCC managing director Martin Talbot said: "Duffy and Alexandra Burke have been the biggest new arrivals on the British music scene over the past year, bar none.
"But the biggest selling singles and albums of the year also show that talent, both new and old, can make an impact, if the music is right.
"Besides the obvious impact of the X Factor artists, including Burke, Leona Lewis and this year's finalists, Duffy, Katy Perry, Sam Sparro and Scouting For Girls all scored big to show that new talent can make an impact."
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