As Richard Wood noted above the factory have confirmed that the immobiliser is indeed the STERLING EXCEL TRANSPONDER IMMOBILISER.
I have sent these details to the insurers in France and hope that is the end of it.
Thank you also to Waldemar for the link to the French M3W forum - very helpful.
They have been able to confirm the answers to my other questions about an M3W in France, which are :
It is homologated here as a motorbike
No helmet required (has seat belts and one sits in)
Only rear number plate required
No MOT test requirement (same as for motorbikes over here, but I'm sure this will change eventually)
