(Reuters) - Former Beatle Paul McCartney has joined the lineup for a Christmas single raising money for the families of those who died in the 1989 Hillsborough soccer stadium tragedy in northern England, organizers said on Thursday.

Already committed to the song are artists including Robbie Williams, ex-Spice Girl Melanie C, Frankie Goes to Hollywood's Holly Johnson and Gerry Marsden of Gerry and the Pacemakers.

The version of "He Ain't Heavy, He's My Brother" will hit the shelves on December 17 and is among the frontrunners to claim the coveted Christmas No. 1 slot in the British singles chart.

The charity single will benefit Hillsborough families who campaigned for more than 20 years to overturn official accounts of the tragedy that smeared fans, blaming them for being drunk, ticketless, and intent on forcing their way into the packed ground.

Ninety-six Liverpool supporters died after a crush at the Hillsborough stadium in Sheffield, and an independent inquiry earlier this year concluded that police tried to deflect the blame on to fans to cover up their own incompetence.

(Reporting by Mike Collett-White, editing by Paul Casciato)