Thanks also Druid9
I had not considered a possible fault with the ignition, but this would certainly allow the power to be cut, while leaving the lights on.
The ony item which does not backup the ignition fault is the lack of problems when still cold and when idling.
She only seems to cut out when she has warmed up, and is running >1500rpm
I am leaning towards a faulty coil (especially since she sometimes has trouble firing), and will check voltages and resistance overnight.
I think PaulF's suggestion of swapping the coil is also a wise approach, and may eliminate / confirm a cuplrit.
