Good point although a rock is hardly a possesion just a mere obstacle that nobody can claim and therefore can be removed. If the said car on your drive has no insurance or mot or tax and you are caught pushing it on the road who is committing the offence?.I did see it in the online news the other day too.
First though was to winch the car across the street if there was a convenient lamp or telegraph post to use.
I'm not sure how the law deals with objects left on your property and where the duty of care extends to with respects to that object. As far as I know it is a motoring offence to block someone's access. Are cars considered the same as other objects? Is it the same as storing a big rock on someone's drive?