The song does have a Manchester origin, and it was sung in Manchester at one time. I remember a correspondence in the 'postbag' section of the Manchester Evening News, sometime in the 1960s, I think. The original lyrics of the song were given by some readers, and it certainly appears to be have been current in Manchester around the turn of the century. Perhaps a resort to the Local Studies, Manchester Central Library, or to the newspaper's cuttings files might turn it up.
   My guess is that it was a local music hall song, probably from the 1870s or 1880s. 'Pomona' refers to an old Manchester resort - pleasure gardens that had a rather rakish reputation. They were swept away by the construction of Pomona Docks in the 1890s.
   Somehow, the song appears to have migrated to the West Country. There were shipments of china clay to the port of Manchester, and Pomona Docks were used by coasting craft, so maybe that's the connection. After all, Pomona is easily adaptable to Lamorna.

    Regards,
    Train Guard