Hi Hinch and welcome to the forum.
I've moved your thread to OTHER TELCO SERVICES as that's more suited for the topic.
Your question is a hard one to answer, I don;t think he has the right to ask you to remove the tinsel as it's simply not his wire but BT's.. But if the wire was damaged then BT would probably come knocking on your door as in effect you have messed with the wire.
The fact that the wire is over your car/garden/property doesn't give you any rights to it, the only time you can complain is if it's within a certain distance from your property but I think it's only a couple of meters. Best bet is to probably ask on the
BT forums as VM users don't tend to have this sort of problem as the cable is delivered underground