In reply to blackcat:
If you do park on private land without permission then you are committing trespass. The landowner, which may or may not be the old man, could sue you. However the damages awarded are likely to be minimal to the point where it isn't worth the bother.
They could call the police who will probably point out its a civil matter unless you are causing an obstruction, in which case they may ask you to move your vehicle.
However if there is adequate signage, then since 2012 (Protection of Freedoms) you are deemed to have entered into a contract and are subject to any terms and fees stated on the sign. You can still dispute these charges fi they are unfair.
Cezza