Interesting point about Lawrence Miles being someone who drops out of projects. I don't think the project was getting stale, really. I think that Lawrence's and Tat's views simply diverged too greatly; the nature of their co-operation had often been nominal, I think, and one person had to leave just to make About Time 6 (for which I am patiently waiting) coherent.

As I've said before, these books are a great missed opportunity. Read as a conversation between two fans in the pub they are very entertaining and informative; "ambitiously definitive", they are not, though they could serve as the framework for one after extensive factchecking.