The location is almost certainly Canada Dock, Liverpool - I used to live close by & often walked through that (then) abandoned tunnel. Road & farm vehicles were often used in small industrial sidings or docks, when the rails were inset.
Are you saying I like "a bit of slack" ? You had better hope Mrs S doesn't see this !.
Unusual but not rare back in those days to see a bit of cable, chain or even rope used thus. Sometimes used to move rail wagons into a restricted spotting place, by driving alongside but ahead of the wagon with the cable running diagonally. Probably not 'Elf & Safety approved these days.