Here is a page about this (with a sound file and video). It indicates Eric Winter who edited "Sing" as the author, and it was published there anonynmously, and Eric was the editor. It might have been printed earier though, shortly after the crash, on the Manchester Evening News letters page - it ought to be possible to check that out. In which case the attribution to Eric might be a misunderstanding.

Tune is the one Ewan McColl used for the Ballad of John Axon, which has led a lot of people to assume the song was written by Ewan.