Teenage Scottish pop singer Leon Jackson should have a Christmas to remember.

Jackson, the surprise winner of Britain's X Factor reality TV show on Dec. 15, is poised to claim the coveted Christmas No. 1 slot on the Official U.K. Singles Chart with a cover of "When You Believe", according to mid-week sales indicators.

Syco digitally released the single on Saturday, Dec. 15, directly after Jackson beat bookies' favorite Rhydian Roberts to win the series four finale. "When You Believe" is a reworking of the popular 1998 hit recording by Mariah Carey and Whitney Houston, which featured in the film "The Prince of Egypt."

On download sales alone, the track is well ahead of Katie Melua and Eva Cassidy's current chart-topper charity cover of "What A Wonderful World" (Dramatico), and Leona Lewis' "Bleeding Love" (Syco), which was dethroned after seven weeks to sit at No. 2 on the current chart, published Dec. 16.

Combined sales of the digital and physical version, which is only available in stores from today, are on target to sell 250,000 - 300,000 copies, good enough to earn honors as the fastest-selling single of the year, says a spokesman for market-leading music and entertainment retailer HMV.

Festive standards will also make a strong showing in the chart. Downloaders are driving chart returns for Christmas classics such as the Pogues feat. Kirsty MacColl's "Fairytale of New York" (Warner Bros), Mariah Carey's "All I Want For Christmas Is You" (Columbia), Wham's "Last Christmas" (Epic), Wizzard's "I Wish It Could be Christmas Every Day" (EMI), Slade's "Merry Xmas Everybody" (UMTV), Shakin' Stevens' "Merry Christmas Everyone" (Sony) and Bing Crosby's "White Christmas" (MCA).

If Jackson tops the singles chart over Christmas, he will be the third successive X Factor winner to do so, following Lewis' "A Moment Like This" in 2006, and Shayne Ward's "That's My Goal" in 2005.