The charity single recorded by the X Factor finalists could become one of the biggest-selling releases of the decade, according to figures out today.

The single – a cover of Mariah Carey’s hit Hero – has been recorded for The Royal British Legion’s Poppy Appeal and Help for Heroes, a charity that provides support for wounded servicemen and women.

It is already certain to land this week’s number one, removing Girls Aloud and their new single The Promise from the top spot.

Hero is expected to sell more than 300,000 copies across the UK this week, but as many as 500,000 singles could fly off the shelves if stock does not run out.

The finalists premiered the single on Saturday night’s ITV1 show.

HMV spokesman Gennaro Castaldo said: “This is proving to be one of the biggest single releases for years if not the decade.

“Only Leona Lewis’s debut hit A Moment Like This, which sold over 500,000 copies in its first week, can compare.

“It’s selling more than most Christmas number ones would, and HMV has placed an urgent order for more copies.

He added: “Hero has sold over 100,000 copies in its first two days alone, and the only thing that may hold back sales this week is whether the manufacturers can keep pace with the growing demand for the CD single, although the option to download is always there.”

Or CLICK below to watch the finalists perform Hero on The X Factor