Talk about money-grubbing ! This CEO must have been desperate to make his PCN target for the day. I think you'd win at London Tribunals on this one, as your wheels are just on what used to be the white line that outlines the bay.
However, you'll have to stand your ground and be willing to risk the full PCN penalty. Going to adjudication is a double-or-quits gamble, I'm afraid. Whilst we on this forum can indicate your chances, we cannot predict the outcome.