Hi Dave,
I've not had prior experience of the selection process myself, but my understanding is that it has changed quite a bit over the past year. I've recently finished all three stages (just waiting to hear the outcome now). You can find posts I put up about all three stages on pages 214 (post #4272), 232 (#4625) & 244 (#4867). I believe that the descriptions of each stage found in those posts are still current and accurate. There are also some online tests you are asked to do before stage 1, but I don't think anyone is entirely sure of the relevance of these or whether or not the marks have any bearing on whether or not you pass stage 1.
Hope that helps
Pat