LGW Express
When you get your ID, go to the LGW Express ticket counter and you get a staff discount card. When travelling on Thameslink or Southern, show your ID when buyin your ticket at the ticket counter. Unfortunately, I believe that you only get the discount when purchasing tickets from LGW. Ask at Victoria train station.
Word of advice though, when getting the train in for training, try and get to LGW min of 45 minutes before the start of the course, can take a while to actually get to hangar 6.
Good luck!!!