The written exercise was a fairly basic attention to detail test in my case. This was in the form of a 3 page document that had to be checked for punctuation, spelling, format and content mistakes. There were potentially 50-55 mistakes in the document and I was given half an hour to highlight them. Nothing too complicated...
The case study was conducted as a group exercise. The main purpose of this was to analyse the data provided and create a presentation at the end of it. The material shared with us included a summary sheet that described what the client wanted us to present on+ a 12-15 page booklet summarising the company, key issues, performance charts etc
We were given 15 mins to read through the data on our own. After that, the assessors came into the room to observe. We had about 40 mins from when they entered the room to discuss key issues, propose solutions and put together a presentation. The presentation lasted 5-10 mins and this was followed up by 20 mins of questions.
The technical interview was heavily based on the CV, and the specific area I applied for. They did ask several probing questions but as long as you are confident in your area of expertise, you should be fine.
Hope this helps...Good luck with the interview!