Maybe they should have charged a tenner per night parking, instead of telling customers who drive trucks they are not wanted. 
I can see their point if there are trucks parked days on end, (and of course you ■■■■ s who spoil things for others by leaving your mess 
) but some of these supermarket parks are handy to park up, stock up your fridge, get a half decent meal, and use the bog in the morning.
They should capitalise on it instead of alienating a section of their customers.