Just found out that the the Capo didn’t want to start in gear with the clutch pulled in …. so suspected a bad clutch switch. In the end it wasn’t, but I’d pulled the old one and did some homework anyway. The switch is a Saia Burgess V4NCS with an actuator kit on top (QA4). Now a direct replacement seems hard to find, however the V4NS as sold by RS-Components is almost the same and comes with 500mm wires already attached, it even has the same 2.5N operating force.
So for a miserly sum of £7.80 (plus VAT & shipping) a new switch can be clipped into the existing actuator shell and spliced into the old loom – simply cut off the yellow wire (not needed) and 
sheath/splice the other two. A darn sight less than the £70 plus that I’ve seen on the web for an Aprilia item! The only down-side appears to be that the cables exit from the side not the rear ….. no biggie really.
On the other hand if your switch has a bad actuator, then just buy that alone for a whopping £3.24 (plus VAT and shipping). In fact I’m sure that a bit more digging would throw up these items for considerably less …… I just got bored!