The fact he did not answer the door previously would mean I would write a letter to say that he does not have your permission to park in your space. If a car is parked in the space again you will take photos and details to take legal action.
I found this online...
Dear (insert name),
Further to our recent conversations regarding the unauthorised parking of your vehicle registration no. XXXXXXX in my demised parking space granted by my Lease of [ADDRESS], I now give you formal notice that any further incidences involving this, or any other vehicle owned by you, will be considered to be a tort of trespass to land.
By parking in my space, you are denying me access to land to which I have title, which in turn results in a diminution of the value of my property. The Court of Appeal, in Raymond and anor v Young and anor [2015] EWCA 456, upheld an award of damages of £155,000 against a tortfeasor in similar circumstances.
Accordingly, I hold you liable in the sum of £100 for each and every occasion upon which any vehicle belonging to you (or of which you are the registered keeper) is parked in my space. Your acceptance of these conditions will be deemed to have been demonstrated by conduct, and I shall seek recovery of damages by means of civil litigation, and enforcement of any Judgement obtained by means of County Court or High Court bailiffs.
I trust that my position is now clear.
Yours etc,