Hiya,
No idea how tough their selection processes are over there, but generally it's always good to show a little knowledge of the basic operation, in particular what basic type of things you might expect to be doing from the location you are applying for. If you can demonstrate that you have some experience of using the services to some extent that'll probably help also, and perhaps a little knowledge of the kind of trains etc you might be looking at (I'm assuming it's a traincrew position?) but not TOO much knowledge I'd suggest as being viewed as a 'spotter' could be seen as a negative point in some people's eyes.
Above all though it's your general aptitude and abilities they should be interested in, so concentrate on that. Make sure you have some answers in stock for the inevitable "Give us an example of when have you done this or that" questions, and just try to seem like a calm, level headed kind of person!
Best of Luck ;-D
