I've just found out the date of a conference that I'm expected to give a paper at in the spring - I'll use it as an opportunity to mention my work and the other, how they compliment each other and differ, and my developments of the ideas presented in the book. I'll also mention that I've developed ideas that I presented at a conference 6 years ago! (I'm almost certain that there'll be someone at this conference that was at the other, as it's being held at his Uni)

thanks all for the good advice and encouragement.

Ohhh bother! My heart goes out to you. Unfortunately, this happens often, and I've seen with my own eyes! However, all is not lost! Firstly, how close are we talking here? (i.e. are the similarities conceptual/textual, or both). The reason I ask is because, from my understanding, the notion of a PhD being 'original' is often a problematic and debated one. Many PhD students are put off from their original interests due to finding articles in journals which closely reflect their hypotheses (so frustrating when that happens!) However, originality can simply constitute taking a different stance by looking at a concept via a certain text. I sympathise with you, if that's any consolation.