Train 171 721 is a two carriage class 171 diesel multiple unit, in Southern livery, manufactured by Bachmann. The catalogue number is 32-460Z. The real trains (as of October 2015) are still being used by the operator Southern, a very good article about the train type can be found at http://www.semgonline.com/ and another article about the trains introduction can be viewed at http://www.southernelectric.org.uk/news/
This photo is looking over the roof of the depot cabin, the train is berthed in one of the sidings used for the shunting puzzle.
In this picture, you can see that the class 15x and 17x trains just about fit in the platform.