Hi,
My best advice would be to come prepared. They will ask your boyfriend many questions and a lot of these will require fast answers, that's what they like. As long as you have the relevant experience to talk about you should be fine, but come without anything to say and you will pay the consequences. They mostly ask about safety, and as this is a safety critical role, it's paramount your boyfriend has the relevant experience to be able to sound like someone they want. If your boyfriend has no experience in the industry as yet, try and talk about roles in the past, any training he has done to further his knowledge about safety. That's one of the main things. And don't rush, they like you to take your time, and think about things. Take a few seconds to gather what your going to say and then show the Yard Manager why he is the best person for the job. Also make sure you know who GWR are and why this job is available, they like people who know what they are getting themselves into.