At the risk of repeating myself dear lady...
Well yes they can - but they might not.
Your parking history is of no consequence - you've just been lucky for 20 years not to have been chased away.
The person (company) who owns the land can dictate their own parking policy - how they enforce it is another matter - worse of course are the services of a clamping firm so look out for clamping signs next time you park there.
Peccavi², October 2009
