Attended the assessment centre in Croydon; consisted of a group exercise for an hour and then an interview for an hour following that.
The group exercise was to pick a location where a sustainable housing development would be located, and you where given key points to think about and address e.g. materials, government constraints, location, cost etc. We were given 15 minutes to prepare between ourselves in front of two people assessing you, and then you had to present on a flip board to the assessors.
The interview was fairly straight forward, the person interviewing was following a strict set of questions from a framework, and was filling in a box as you spoke. It was quite strange having to stop and start to wait for him to fill in the boxes, word for word. Kind of ruined the flow and how you came across I suppose. Not much eye contact!!
A technical question was asked, about Terzaghi's principle of effective stress, nothing major; what takes the load during long term and short term (undrained, and drained).
Overall was a worthwhile experience, they seem like a good company from how they presented themselves.
ADVICE - do not learn facts and figures about the company, they give you a short presentation at the beginning, its a waste of valuable brain space. Perhaps put in values of the company during your interview answers, but they wont as you questions on themselves.