I did it last summer, and although I didn't get through (based on the written exam), surprisingly found it one of the nicest assessment centres I had done.
It won't necessarily be the same, but the written exam I did was on the topic of the dying British high street. We were initially instructed to summarise three newspaper articles on it, and then to make notes to brief an associate before their meeting with a fictitious landlord client. I (quite stupidly) spent time summarising each article in turn rather than providing a general summary of all as there was a fair amount of overlap. I also wrote a lot of information very fast as wanted to get as much down as possible but was penalised for typos and they fed back that they expected a more polished document. Based on this, would strongly advise you don't compromise quality for quantity.
They also said you could bring your general knowledge into your answer so general commercial awareness should help.
Is this typed then? Or hand written