Re: 'Cheap' in terms of food, now means selling your privacy too.
"Are Lidl actually collecting it to enforce 90 minute limit parking fines though? "
Not really any different than any other store who gives you free parking for a limited time - but only if you buy something in the store. The ANPR knows you parked there and for how long - the manual check confirms you used the store and when. Presumably you don't have to buy anything - just queue at the checkout. ALDI use the same system on their car park - except it is only for validated customers' use. Anyone not validated gets an automatic fine.
Our Waitrose allows a short free parking period in the community car park if you get your token validated at the checkout. In theory you can't ask for a validation without actually buying something. I don't think there is an ANPR as well - but it wouldn't be that difficult as the car park is covered by at least one town CCTV camera.