Don't worry, I managed to disassemble the mechanism. The nut which needed to be unscrewed was extremely tight and partly embedded in the vee pulley it sits on top of, which made it very difficult to grip properly as the shifting spanner would slip off continually and got very slightly deformed by the nut. I managed to hold the mechanism at the other end of the bolt, (the mechanism which grips the crankshaft?), with multi-grips held in a vice-like clamp I managed to gerry-rig, and sheer brute force and some WD40 eventually budged it, but it took me and my brother both working on it to do it. The nut was so tight, the multi-grips deformed the gripping mechanism (which is made out of steel plates) slightly.
I called it a day after that. I should be able to check the spring and put everything back together how it's supposed to go, and hopefully when it's back together, the vee pulley will retract after pulling the starter cord.
Peter, December 2005