Hi Hannes,
I had exactly the same problem a few weeks ago. For details see here: http://www.talkmorgan.com/ubbthread...-although-indicator-light-off#Post706450
The cause was apparently a defective insulation of the immobiliser ring.
Since the replacement, the problem has not reoccurred (I have driven approx. 3000km since then).
My suspicion: on the left-hand drive Morgans, the space at the ignition lock is very tight. Possibly the ring is damaged over time by the bunch of keys when starting.

Michael
2018 Plus 4 Sport