When you attach the towbar does it just slot in [not needing the key] the green part appears on the lock and i cant get it to drop, is the key only needed to detach the towbar, hope that reads ok, cheers.
no key opens lock to fit hitch also locks in position to stop theft and pulling out when towing
Most people leave in position while on site and out for the day.
I have only seen about 3 other vehicles with removed tow hitch beside my own which is removed soon as van is unhitched and put in boot.