How do you know that? do you mean you've never SEEN this happen whilst you have been in Sainsbury's? Whats to say it doesn't happen?

and you ask if the chav element is generalised to Tesco's nationwide - could it possibly be the chav element in question could be localised to your area? Have you had this same problem in the majority of Tesco carparks across the nation? If no, then I can't see your argument?