Some great information here guys, thanks so much. I am in Englandshire, the property is a town centre semi commercial (flats above a cafe.
plan of attack so far is, speak to planning, suggest to the a-hole that I’ve located the actual owner, put my own padlock on the gate with a note asking for a conversation about the continued shared use of the area, get the legal cover from insurance to begin litigation for restricting a prescribed easement, investigate registering an interest with land registry (I think I can only do this if it’s a registered property though)
really appreciate all of your help and advice so far, teamwork makes the dream work 🙌🏼