Mr Mustard has more experience than me, but I think this is thin gruel, as I'm not sure adjudicators are of one mind on this one, bearing in mind it is a Regulation 9 PCN, so served at the roadside to the vehicle, (or driver) as soon as the PCN is printed. Certainly the council won't give way so you's have to risk the full PCN penalty at London Tribunals for an unbiased decision.