I was given a weeks notice that I was coming in for an assessment day at TfL and that I would be expected to prepare a presentation for the day, My presentation subject was the Thameslink Programme at London Bridge and basically how I would carry out the works. On the day there was also a group exercise which involved deciding upon the best engineering proposals to take forward. Then we moved into a written exercise which was incredibly vague and open for a huge variety of interpretations. This was by design. Then came the presentation, which I felt very unprepared for, 15 minute presentation, followed by 15 minutes of questions, it went surprisingly fast. The day ended with an interview which was made up of competency based questions and a few technical questions. Overall my suggestions for anyone attending an assessment centre would be to prepare for the presentation and interview, the other two are impossible to prepare for. In the group exercise do not be silent but don't talk too much, and make a point of showing the observers that you are actively watching the time.