The BR class 38 seen here is a one-off prototype. Engine number 7939 was made in 1989 to compare a Metro-Cammell made class 38 to a Brush Traction built class 60. The class 60 won the contract, and subsequently Metro-Cammell was sold and closed. The single class 38 soldiered on until 1997, when British Railways was fully privatized. The engine was then sold with a number of spare parts to Lego Rail Transportation Society, which has kept the engine running ever since.
In the real world, the class 38 was never built. It was proposed and then dropped in favor of the class 60, which is what I based the story on. Metro Cammell really existed and was dismantled in 1989 sometime after loosing out to Brush Traction for the class 60 contract, and everyone knows that British Railways was taken apart in the mid-1990's.
The Lego model, however, is a mash-up of a William Howard's diesel locomotives and the 2010 official Lego set 7939. the model is power-able via 9v (not included) and as it features two trailing pony trucks, is meant to only go forwards.... I assume that it could go backward, but with great difficulty.
The rear of the model. The numbers "7939" go on printed 1 x 1 tiles under the head and tail lights where the exposed studs are.
The locomotive bears a strong resemblance to Lego set 7939, and with good reason. I consider the left loco to be a bigger cousin of the official model on the right.
(the smaller loco is NOT included in the LDD file!)