In the first instance, the registered keeper is the first point of contact for the PPC. The RK has two main options (but there's also a third). Keeper can either admit to being the driver or keeper can name the driver (if it genuinely was someone else). Once the keeper has named another (legitimate person) as being the driver then the keeper is no longer liable, irrespective of whether or not the PPC gets any money from the driver. In other words, if the driver then fails to respond they can't lawfully go back and chase the registered keeper for the payment because by naming the driver the RK has fulfilled his legal obligations.

Now either the admitted driver must in the first instance appeal to the PPC who issued the ticket. If that appeal is unsuccessful, then the driver can lodge an appeal with the IAS (lodging such an appeal with the IAS will cost the PPC £27 for each and every appeal). If the appeal finds in the driver's favour then that is legally binding on the PPC and that is the end of the matter - full stop. If the appeal finds in favour of the PPC, then that is not similarly binding on the driver and if the driver still refuses to pay then the PPC must take the driver through the Small Claims civil courts to get its money.

One concern that I have is that the PPCs may well try and incorporate the £27 IAS fee somewhere into the threat-o-gram process as an additional escalating fee - and I have no doubt that if they get an IAS appeal judgement in their favour then the follow up threat-o-grams will have that as an additional recoverable 'cost' if they go to court. The third option is the RK, who was not the driver, refuses to name the driver and challenges the legitimacy of the ticket through the PPC appeals and then IAS appeals process before deciding whether to name the driver or not (if ever) or eventually just pay up themselves.