People seem to be complicating what, for me, is a very stark, simple picture of any industrial town, in this case in the first half of the twentieth century. As with Jim Lad it is very much like the city (Liverpool) I grew up in. Whatever the origins of the word, the gasworks croft was simply a piece of waste ground where courting couples used to go for privacy in a busy urban environment. I remember what we called 'the rec', which I think was short for 'recreation ground', a few hudred yards away from Liverpool Football Ground, which was a favourite meeting place for couples when I was growing up.
The train 'setting the night on fire' was a steam train; it was possible to see into the driver's open cab where he and his mate would open the door of the firebox and shovel coal in, lighting the night up. Anybody who has seen the documentary film 'Night Mail' will know exactly what I mean   
I can still remember Salford the way MacColl described it before they knocked down the old terraced houses and smoke blackened factories and put up the soulless high-rise flats.
MacColl's attitude to his childhood and youth in Salford was very much love-hate, as was made clear in Tim May's film, and this comes over perfectly in the song, which is why it is such a good one.
Jim Carroll