Hi Kate!
Well Done!
It's pretty much a group interview. You will be interviewed with maybe around 30-35 others, put into groups and assessed on group activities and most probably get asked a random question where you'll have to go up to the front of the room and give answers. The panel are all so lovely though and they take notes of EVERYTHING so be aware of not just how you answer the questions, but how you present yourself at all times and how you interact with the other members in your group. But in saying that just try to act how you normally would, it's hard because you're nervous but they can see through a 'fake personality' so just act accordingly to YOUR personality even if you clash with someone else. It goes for 2-3 hours and if you get through you will get the 2nd interview later that day or the next. Good luck!!!
