I have ignored these in the past, appealing, complaining or whatever is entering into a contract with them, as soon as you do that you are on the way to accepting liability, it is an idle threat of court action, (they use the term 'MAY result in county court judgements blah de blah....). stick any correspondence in the Vera Lynn, I've ignored several over the years inc one from The Asda car park in question.
Parking Eye, Excel, UKCPS and a number of others take regular court action now.