It was 6″ into the lane and now you’re saying its 3″ into the lane… Basically if you knew it was taking up more space than was strictly yours for all those years I think you have been asking for this day as the neighbours probably think you are a bit of an ass hat for making their lives harder.
Problem with neighbourly tiff’s is that grown men are scared to talk to each other and it all becomes ridiculous…
If you don’t see that side of the hedge or use that lane… but others do want to drive down it then why not sell it to them like you mentioned and put a fence or wall up or whatever you want on the new boundary.
They get the access they need to a property they’ve had all their lives.. you make a few quid and get a proper boundary and no one thinks you’re a dick (whether you are or aren’t).
It’ll save some hassle all around… if the conversation with the neighbours goes sour then go to plan b.. land mines, dog shit bombs, razor wire, shitting on his cat ect..