With regards to GlosMikeP's point, I agree wholeheartedly. At the end of the interview phase, they ask you to confirm your choices, in order of preference. I had put down several, including WSO and Air Traffic, as well as pilot at the top, on advice from the AFCO. In the intervening period I had given it careful thought and decided that if I couldn't fly, then I didn't want to be forced to be around all the action for the remainder of my career. Thus, when asked to confirm my choices, I said I wanted pilot, nothing else. They seemed slightly taken aback at this, but I confirmed that it was my considered intention, and in the end, thats what I got!
I can also endorse the recommendation of The Econoist's online service. It does require a paid subscription, but its well worth it! The advice I was given was to prepare half a dozen stories in each of four categories, local and national for past months and past years. The Economist subscription allows you to track news stories all the way to their roots, so makes reseach for this a doddle. Remember, they want your opinions on the matters you are discussing, that you have formed yourself, and are able to defend with rational and balanced argument.