It's a contract, not a fine
Private parking charges are not a fine — they are a contractual claim. The operator must prove (a) you entered into a contract by parking on private land where signage was clear and prominent, and (b) the charge is not an "unfair penalty" under the Consumer Rights Act 2015. ParkingEye v Beavis [2015] UKSC 67 settled that £85 charges with clear signage are usually enforceable.
Keeper liability under PoFA 2012
If the operator does not know who was driving, they can only pursue the registered keeper if they strictly comply with Protection of Freedoms Act 2012 Schedule 4. The Notice to Keeper must arrive within 14 days, contain specific mandatory wording, and meet other procedural tests. Any defect breaks keeper liability entirely.
BPA / IPC code of practice breaches
Every accredited private parking operator must follow the British Parking Association (BPA) or International Parking Community (IPC) code. Grace periods (usually 10 minutes), signage standards, charge caps, and appeals procedure are all specified. Operator breaches are themselves appeal grounds at POPLA (BPA) or IAS (IPC).