Sam Larner once explained that in the old days in coastal Norfolk, the press gangs used to go from house to house searching for 'recruits'.
The older houses had large fireplaces (you can still find them in Ireland) and some of the local people fitted metal rods into the chimneys so that, when the 'gangs' were in the area, a likely victim could climb up and stand on the rail until they had gone away
He associated the practice with this song.
Walter Pardon lived three miles from the coast and a fair distance from any significantly sized coastal town, but he had also heard of the practice.
Jim Carroll