His convenience or lack thereof is not your problem.
If he had come to you hat-in-hand asking for permission, and then followed up by numerous gestures to indicate he understood the magnitude of the favor (bottles of wine, a voucher each week for you to dine out, perhaps making a pleasant improvement to your garden while he is at it) it MIGHT be understandable.
To go behind your back is bullshit. I would tell the landlord you need the driveway ASAP for visiting relatives, for a childminder or whatever other reason you think of and force him to clear out. He didn't much care about maintaining goodwill with you, did he? So why should you worry about it?
Otherwise you will be established as the neighborhood doormat.
I have a cottage in an area where one house's extra-large side lot was for a couple of decades treated like community property, because the owners didn't care and were an elderly couple who enjoyed watching the activity.
Volleyball, croquet, kids playing, overflow space when neighbors had barbecues, or just as a convenient shortcut to one another's homes. etc. Well, guess what. When that couple died and new owners
took over, we all became scrupulous about not setting a toe on that property, because we didn't know them and we did not have their permission. They clearly like more privacy than their predecessors and that is fine. We didn't say to ourselves "those newcomers will just have to put up with us because we have been here longer and "own" the neighborhood!" Which is what your "neighbor" is doing to you. Disrespect.