Duffy comes from the town of Nefyn in north-west Wales Sound of 2008: Duffy

The rising Welsh star entered the chart at number one last week with Mercy.

H Two O featuring Platnum's What's It Gonna Be rose five places to number two, pushing Canadian band Nickelback from second place to third.

Join With Us by The Feeling went in at number one in the album chart, while Amy Winehouse is at number three.

The troubled singer, who has recently performed at the Brit Awards and won five Grammys, was at number 14 last week but her recent successes have boosted her sales.

UK SINGLES CHART 1. Duffy, Mercy 2. H Two O Feat Platnum, What's It Gonna Be 3. Nickelback, Rockstar 4. Basshunter Feat DJ Mental Theo, Now You're Gone 5. Kylie Minogue, Wow Source: Official UK Charts

Nickelback stayed at number two in the album chart with All the Right Reasons.

Jack Johnson, who topped the album chart last week with Sleep Through the Static, was down to number eight, while Michael Jackson's Thriller 25, the 25th anniversary reissue of his iconic album, was down three places to number six.

Former G4 tenor Jonathan Ansell's solo debut, Tenor at the Movies, was at number nine.

UK ALBUM CHART 1. The Feeling, Join With Us 2. Nickelback, All the Right Reasons 3. Back to Black, The Deluxe Edition, Amy Winehouse 4. Mark Ronson, Version 5. Life in Cartoon Motion, Mika Source: Official UK Charts

Back in the singles chart, the BBC's Sound of 2008 winner Adele's Chasing Pavements fell one place from five to six, while David Jordan's Sun Goes Down was down three to seven.

Brit winner Mark Ronson was up from 22 to 13 with Valerie, featuring Amy Winehouse.