That sign is incapable of forming a contract with the driver as it is forbidding.
1. No offer, so no contract. The wording is purely prohibitive (“NO PARKING/NO STOPPING/NO WAITING/NO LOADING OR UNLOADING”). Contract formation requires an offer capable of acceptance. “Don’t do X” cannot be accepted by doing X. At most it’s trespass, which only the landholder can pursue—and usually only nominal damages.
2. No consideration. The operator provides no permission or service in return. Without consideration flowing to the driver, there is no contract.
3. Beavis is distinguishable. In Beavis there was a clear permission to park (2 hours free) with a prominent price-term for overstaying. Here there is zero permission: the charge functions as a deterrent/penalty, not a contractual price for a permitted service.
Judges have occasionally taken the “by stopping you agreed to pay £100” line, but those decisions usually turn on signs that actually offer a permission (however limited) or use coherent “contractual fee to stop” wording. This sign doesn’t: it is prohibitive from top to bottom. The proper cause of action would be trespass, which only the landowner (not a contractor without proprietary interest) can bring, and damages would be nominal, not a fixed £100.