Thanks for the replies, very helpful and should be enough to sort out the insurance.
It may be just a French thing because I had the same with my motorbike (different insurer). They wanted it to be "engraved", and to see the receipt for the SRA approved lock that I had to fit to the bike when parked. I imagine SRA is the French equivalent of Thatcham. I already had a very good lock and wasn't going to get another one so in the end I downgraded the insurance from TPF&T to third party only. I live in the middle of nowhere and rarely use the bike anyway.
My insurance came out cheap because the M3W is regarded as a bike and I have nearly 50% no claims on motorcycles.
This is the bike :
