Has anyone here applied to sit a Part III paper on an area of their own choosing, e.g. not even on the notes of a course given in a previous year?
If so, I'd be interested to hear your experiences. I've read Tom Körner's guide, and sitting a paper on material in a chosen book, on an area not taught at Part III, seems as if it could be amazingly useful preparation for doing a PhD.
What kind of help do you get, or obstacles do you experience, in choosing a field, getting a paper set, and then studying the stuff?