Whilst sitting in the garden enjoying a bottle of Palmers' "Tally Ho" I've been having a rummage round to try to get to the bottom of this. The first thing I discovered is that Section 56 and Schedule 4 of the Protection of Freedoms Act 2012 does NOT apply to parking tickets issued by local authorities (quite the opposite of what I said yesterday!). So, all of what was debated yesterday is null and void because, as I understand it, the ticket in question was issued by a local council.
Such parking penalties are enforced under the Traffic Management Act 2004. In its guidance (which runs to more than 180 pages!) there is a simple statement under "Collecting Penalty Charges". This simply says "The penalty charge is usually paid by the owner of the vehicle unless the vehicle was hired at the time". It goes on to define the "owner" as ‘"...in relation to a vehicle, means the person by whom the vehicle is kept, which in the case of a vehicle registered under the Vehicle Excise and Registration Act 1994 (c. 22) is presumed (unless the contrary is proved) to be the person in whose name the vehicle is registered."
All the rest of the document where dealing with parking charge collection refers to action being taken against the owner and no provision is made for the owner to pass responsibility for the charge on to anybody else.