I've just fiddled around on Google and found some photos etc; it seems to be quite a sizeable freight building, but rail tracks don't enter the building. There appear to be a couple of sidings, but little else. Let us know what you find!
Here's a couple of references:
http://www.railbrit.co.uk/location.p...halling%20Yard
http://en.wikipedia.org/wiki/Tinsley_Marshalling_Yard