Welcome to the thread...!!
Another Plus 8 owner is always very welcome: we are quite a rarity here!
An unfortunate little accident, 6.5L of hot oil is going to go a long, long way!
But because the RAC deemed it to be a traffic accident you would probably had grounds to make an insurance claim, and then your car policy underwriters would then have claimed on the third party insurance of the owners of the drive.
In the litigation riddled world in which we live everyone is responsible for all their property and their actions!
BTW, do you have a photo of the sump shield you designed and had fitted?