Pass some online tests and you get to the assessment centre. For the group task, you get given a case study with a situation and asked to come up with a creative solution which you all agree on. Some characters are more dominant in conversation than others, and I sometimes had to fight my way in to say something. However, everyone is fairly mature. You then have to present the agreed idea to the assessors (and are all forced to speak here).
The written task involves reading two arguments about an impending decision, and justifying which you say you prefer. It's harder than it might seem to complete it in the time they give you (50 minutes).
The interview is competency-based, so if you don't have enough to say you'll struggle, but my interviewer was very friendly which helps put you at ease.