Aha, so it's "by the gasworks CROFT"

I always sing it "by the gasworks CALL" (assuming th gasworks had a whistle or siren to call the workers.

It really annoys me when people sing "by the gasworks WALL". A very unimaginative way to rhyme with "factory wall" !

@David el Gnomo, I love that version on 'The Rough Guide to Scottish Folk', sung by the man himself. Must listen again for the "Croft" reference.