Finally sorted the problem which might interest any of you who use the clutch.
There is a small plastic pin which moves through the clutch lever bracket and pushes on a contact switch when you squeeze the clutch lever. This either makes or breaks a circuit allowing you to start the bike in gear while the lever is held in.
I found that the plastic pin had actually worn down to a point where it wasn't long enough to make contact with the switch, which was working fine when I tested it in isolation.
I have replaced the pin with a 3mm diameter piece of nail, galvanised of course, and all well again.
I initially thought it would be the switch I would need to replace which is A$150! Ouch!