I wonder what all the other neighbours think about your massive, albeit "neatly trimmed" hedge. Sticking out a metre beyond your property line, is taking the mick a bit. And look where it's got you - nothing but bad feelings, and stress, which has now escalated to police involvement.
All of which could have been avoided by you just cutting the ruddy thing back and parking where any normal house owner would.
For the sake of your two disabled adult children, if nothing else, I would be taking the shears to that hedge. Then see if the neighbour "from hell" leaves you alone.
Until you do this, you'll never know if he really is "from hell" or just got his codpiece in a pucker over a car being parked in an inconvenient place.
Once the hedge is back to a reasonable size, and the car isn't parked where it ought not to be, then your neighbour should be more than happy to just leave you alone. And if he's not, then you've lost nothing, but gained space outside your house, and as the police are already involved, then they can carry on with their investigations
Honestly, with all the crap going on in the world, I can't believe this has escalated to this point because two neighbours have both dug their heels in. Over a flipping hedge and a bit of unadopted road. Pick your battles. I really don't think a hedge is worthy of this much aggro.