This may be called a parking charge notice or fixed charge notice either attached to the windscreen or as a notice to keeper/owner through the post? There is no legal obligation to pay these charges as they are not fines or penalty charges. However they cannot simply be ignored and you must take action as private parking companies (or the landowner) can pursue a claim for damages in the small claims court. As demonstrated when Barry Beavis fought his parking ticket to the Supreme Court, these are often enforcable, but can be easily dealt with if you act fast.
Paying your parking ticket will cost you anywhere from £40 to £100, and if it gets to court it could be up to £350. That's per ticket!
T&Cs apply, BPA companies only.