As said before, check out The Economist. They've got a good website, with many in-depth pieces. Worked for me!
Maybe not always, but in my case the interviewer seemed to steer away from the hottest current affairs' topic, as it seemed to be the one everyone was reading up on. They asked me what was going on, nationally and internationally, and quizzed me on one of my chosen special subjects. Hence know enough to get by on anything you mention at that stage, I'd say.
Oh, and as people have said, don't bull****. They'll keep asking for more info, and if you run out of jazz, tell 'em so!
Good luck!