I have noticed this also, just the ruts not the vehicle, this section has become very hazardous especially when it’s wet or if there has been a frost, might be worth e-mailing the council about to see if they can do anything with it?!
He regularly walks his dogs in this way because he has a bad back.
This section of Icknield way still seems to be byway. So I believe you can legally take any vehicle you like down that part.
I have found if I ring my bell, he always moves the van as much to one side as possible, though on much of the track that still doesn’t leave much room to pass.