Also known as "GWR" or "Great Western Railway", this is another song from the Academy Award winning 1975 animated short film Great. The Great Western Railway was one of the first railways to be built; founded in 1833, it linked London with the West Country and Wales; it was engineered by Isambard Kingdom Brunel, who is the Great alluded to in this film rather than the railway.
"G.W.R." was also the B Side of the August 1976 single "Oh Wot A Big One!", and was composed by Jonathan Hodge.
Suggestion credit: Alexander Baron - London, England, for above 2