A matter of emphasis Mike - Jacket - one word, jack it two words.
As with 'Shoals', MacColl made the song directly from interviews with navvies and tunnel workers - he said that this was how the phrase was explained to him - there are recordings of the interviews he did with some of them on our shelves.
It would seen he might have got it wrong, if he did, he and I owe an apology to Adrienne Johnson (but sadly both are dead)
Thanks for the heads up Jack
Jim Carroll