I'm not sure how up to date Dave Yates would be with geometry trends and suspension correction at this point in time, certainly the head tube angle is a lot more relaxed than my Bontragers.... I'll take some better photos, I'm sure that will go some way as to answering your questions! I might also email Dave Yates with the frame number, maybe he can tell me when this was built!
I expect he understands geometry perfectly well, but I wonder whether it might be part of the famous Dave Yates charm to pretend not to. The photo below has been on his website for many years - I think the fork is a 1999 Z1, and the photo dates to about then. However it looks as though the frame is an earlier one designed for a much shorter fork. Note the negative bb drop! And the very 'relaxed' head angle.
Why would you use that photo to advertise your skills in January 2010? Is it some kind of bizarre joke? Is he in a competition with Roberts for who can have the most out of date website? A bit of a character would be an understatement methinks.
Still your bike looks promising to me. Some kind of Columbus, can't quite see which. bb in fact on the low side, suggesting possible potential for longer fork if you happened to prefer. And £135! You drive a hard bargain!