Hi, Point ( 1 ) if the place where you pay to park your car is not sufficiently displaying signpost's advertising that they are not responsible for the theft or lost or stolen property, you may have a claim. 

(2) what is their duty of care of your (property )when you pay to park your car on their land, Did you hide your goods, handbag, property in the boot of your car, did you act responsibly so it would not tempt a theft.? the definition of property is open to interpretation. you bought a service from them, were they negligent

(3) advice from a no win no fee solicitor could help if you have grounds for a claim.

Good luck.