It's definately worth having a browse at the BA mainline interview thread as the format is very similar. The assessment consists of a group exercise, psychometric tests and an interview, but not necessarily in that order.
My interview was conducted by a management pilot and a HR bod. HR asked questions such as tell us what routes do we fly, what issues does the company face at the moment, how many a/c do cityflyer have, how long has the company been going, why do you want to work for cityflyer. Pilot manager asked questions like when was the last time you made a mistake, what did you learn from it, when have you contributed to working successfully as a member of a team, a time when you made a positive contribution to your company, what is the most stressfull situation you have encoutered, a time of conflict and how you resolved it,etc. The whole process was very slick. No questions about current/ previous employer, aircraft, CV. The only questions asked were the ones they read from their notes.
Hope it all goes well.