CTC have so so many questions they can possibly ask - you're in there for about an hour so its not stupidly long, but definitely enough time to see whether you have done your research. Rather than list questions, I'll suggest a few things you might want to know about - anyone else feel free to add:
Know the partner airlines (Base, core UK hubs, Fleet, any merger info, perhaps passenger numbers last year)
Know the role of a first officer inside out! Show them you know you don't expect to be hands on flying the whole time - what other roles will you perform?
Know the key industry goings-on - emmsions, open skies, pilot fatigue, new aircaft in development, security are a few to read up on
I was asked about pilot hours - how many a week/ month can I expect to fly
Some guys have been asked about a specific aircraft - say the 757-200. How many seats? What might be a typical route?
Maybe know a few technnical bits - why are we seeing winglets on new aircraft more and more? What are wing fences designed for?
Most importantly though, know yourself inside out. Have examples (more thasn one I would suggest) for each of the core qualities, and perhaps try to find a way of linking them in the interview if you find that might help you.
I could go on all night but I think its only fair you do some of the work yourself!
One other hint I will offer - I would advise that you prepare a little intoduction speech as thats how the day begins. Only 3 mins or so but I got the distinct impression that they prefer a bit of detail rather than a quick hello. Cover flying experience, education, employment briefly if relevant. Just a summary but try to be as confident as possible - its one of the hardest bits of the day so prepare!