This was at the end of the Spring Week I attended (we did an assessment centre for a summer internship for the next year). Assessment centre had 4 parts - 2 interviews with employees from the division you applied for (in my case, it was Research), a group activity and an individual activity. There's a competency and a technical interview, so for the competency one, just be prepared to have good examples (and use the STAR technique because they'll have a list of questions that they go through. For the technical, I was also asked quite a few competency questions. The technical questions he asked were not too bad, just keep updated on current affairs - I was asked about an interesting article I had read recently and whether there were any stocks that I would invest in right now. I was also asked two brain teasers - can't really prepare for these, they're not expecting a definite answer, more interested in how you would go about finding the solution. Zero questions about my CV! Interviewers were very nice and easy-going. For the individual activity, we were given about 30 minutes to read about a company and prepare a presentation (basically a SWOT analysis). You present to an employee who will follow up with questions. I can't remember the group activity but just make sure you make a decent contribution to the group discussion.