OK, to clarify... For a Motability customer, although the vehicle is leased from Motability Operations Ltd, the customer is the Registered Keeper, as the V5C is issued in their name and address. They are also technically the Hirer, but this distinction is not relevant for the purposes of PoFA where the DVLA records them as the Keeper.
Any Notice to Keeper (NtK) must therefore comply fully with all the requirements of Paragraphs 8 or 9 of Schedule 4 of the Protection of Freedoms Act 2012 (PoFA) in order to hold the Keeper liable. The Hirer provisions under Paragraphs 13 and 14 do not apply where the Keeper's details were obtained directly from the DVLA.
If the operator fails to meet the conditions set out in Paragraphs 8 or 9, no Keeper liability can arise, and the Motability customer is under no obligation to identify the driver. When challenging a PCN, the Motability customer should describe themselves as the Registered Keeper, not the Hirer.