Well I found the starting problem - the 22 connector (RH switch gear) had a loose wire, preventing the starter button working. Must be just a massive coincidence that it broke at the same time, unless, I don't know actually, but anyway, that's fixed.
I measured the battery while off - 12.7v , and then while running, and it was less, and continuously decreasing to eventually under 12v, so I suspect a charging problem, and not necessarily a dying battery. I measured the volts from the regulator at the 77 connector and that was reading quite erratically, 6v - 7v, sometimes dropping to 1v or 2v.
So next I will test the stator and regulator, but today I was sidetracked due to some unexpected smoke from around the airbox, which seemed to fix itself after removing the airbox plastics, finding that it was coming from a square vent behind the rear throttle body (and nothing electrical), then putting the airbox back on. The vent recirculates the air (including smoke in this case) back into the airbox through a little foam filter, which brings me to my next question... Does this vent normally smoke? I suspect not, in which case I have another issue. But if if it does normally have a bit of smoke, then somehow that vent just unsealed whilst I've had it apart, and then removing the airbox and reattaching solved that loose seal connection.
I can't tell exactly where it vents from, but it seems like it joins the left hand side of the rear cylinder head. Here is the smoking...