First stage: One hour technical test and if passed, a short group session with HR. The test was pretty evenly distributed between maths, logic and object-oriented programming. Some questions are tough but the math ones are pretty straightforward. The short group session was more towards an ice-breaking session between the candidates who have passed the test.
Second stage: Phone interview with one of the deputy directors of the GDC. Emphasis on technical skills and programming know-how. This was as far as I made it.