Group discussion at Virgin: normally there is a group about 8 of you in a room, and you get given a story. It's usually something along the lines of your boat has sunk and you have to pick which objects are the most important to survive, or the world is about to end and you have to choose from a list which people you would save. You get given a few minutes to make your own rankings, then you all discuss it as a group and try to reach a consensus together. It's a good way of seeing which people are too quiet or timid to get their voice heard, and which people are too dominant. Communication and team working skills are vital when working onboard so thats what you need to demonstrate.
With the role play you're thrown into the kind of situation you can expect to face as a TM. In the scenario, you are the TM and you are dealing with one or more customers with various potential problems. Again, you need to show good communication skills, and also be able to demonstrate excellent customer service skills.
Good luck anyway, the guys up at Crewe are very nice and they'll try and relax you as much as possible for the test. A lot of externals have been taken on lately for jobs that were open to internal staff as well so if you can show the skills that virgin like (be open, positive, and customer focused) you've got as good a chance as anyone.
