Hi All,
Thought I'd share my experiences from stage 1 in February at London, I was alongside one other candidate throughout my afternoon.
Interview: This was pretty straightforward, 30 mins HR related questions and 30mins of Technical. I was a complete novice and the questions were in my opinion suited to my capability, however if I were to do it again I would read more than just the amount you think is right, go further and more in depth than the JKI booklet provided.
Reasoning: It was based on the Raven's matrices as mentioned on numerous occasions in this forum, just practice on it till you feel comfortable.
Personality: Just be honest and you will be fine, lots of questions asking you to rank sentences that describe yourself.
JKI Test: Revise the hell out of the booklet and more importantly understand the concepts and how things work with the aircraft.
Well, it's not much of a thorough review, but of what I encountered during the day.