An update for those interested. I haven't had a reply yet, but have been a busy bee nonetheless.
I have been in contact with the store manager. Sainsbury's don't make email addresses public, but you can look up the store manager here :
https://stores.sainsburys.co.uk/. Their email syntax is [firstname].[surname]@sainsburys.co.uk. So if you were to look up the general manager and find out it was Joe Bloggs, the email would be joe.bloggs@sainsburys.co.uk.
The manager was quite helpful, and eventually did help (I did harangue him somewhat, apologies...) in getting them to cancel, and asking them to stop ticketing people for being in parent/child bays unless the child is clearly over 12. Also to get on with processing my damn SAR. If people get Sainsbury's tickets, please do contact the manager, hopefully this will be such a nuisance they stop using ECP, or at least tell them to stop issuing PCNs by hand.
There are two ongoing things:
1) The refusal to comply with a SAR despite a photo driving licence with address being given as ID. They want a V5C, which is nonsense as there are many reasons someone may not have this, and anyway a SAR is a request for details about a person, not a vehicle! I have started a complaint to the ICO and if anyone else reading this comes up against their ludicrous V5C requests, please do the same. I have noticed that Parking Eye also state on their website that they ask for a V5C for SARs.
2) What I asked the manager for was not to get them to check the ages of children, but to stop them ticketing people for "not being accompanied by a toddler" when the signs (i.e. contract) state "child up to the age of 12". I think this is a big deal, as if we consider a toddler to be between 2 and 4, they are currently ticketing people who are quite legitimately parking there while with a child between 5 and 12 (or a baby!) - i.e. probably the majority of parents. I am wondering whether to take this further, perhaps contacting someone as high up as possible at Sainsbury's. I would love to make it so that they are prevented from issuing in person.
Any thoughts?