Her Mercy single sold 40,778 copies last week - just 302 more than Lewis' double A-side release Better In Time/Footprints In The Sand - putting her at the top of the chart for a fifth week in a row.

According to HMV's mid week charts, Duffy will retain both the number one single with Mercy and No1 album with her debut Rockferry.

Leona Lewis, who has recorded the official Sports Relief single Better In Time/Footprints in The Sand will be disappointed not to make the number one spot after her smash hit single Bleeding Love spent seven weeks at the top of the chart last year.

However, it's not all bad news for Leona as her debut album Spirit looks like it will climb back into the top 10 album chart.

Leona has also made headlines this week after her recent trip to South Africa on behalf of Sports Relief.

The X-Factor star visited a variety of programmes and projects around Johannesburg confessing that the experience had changed her outlook on life.

Consequently she is auctioning the dress that she wore during the BRITs on ebay, with all proceeds going to the charity.

Richard Atkins, manager of HMV Donegall Arcade in Belfast, said: "It is great to see such a tight competition at the top of the singles chart this week.

"Duffy's single Mercy has been one of the break through records of the year so far and it's a sure sign of her popularity that she can contend with Leona Lewis.

"It's important to remember that Leona's Bleeding Love single was able to hold off competition from some of the biggest chart acts last year.

"Take That, Westlife and even Kylie Minogue couldn't knock her off the number one spot.

"If Duffy can hold on to the number one spot in the face of such competition, she could well be one of the biggest artists of 2008."

Last week's number two, What's It Gonna Be by H two O featuring Platnum, slipped a place to three.

Elsewhere, Panic At The Disco's Nine In The Afternoon entered the chart at 13, while Elbow's Grounds For Divorce hads a debut at 19.

Both Sugababes and Girls Aloud make gains on the chart, with the former's Denial leaping from 34 to 15 and the latter's Can't Speak French climbing from 20 to 16.