All the Lewisham car parks, and many other (such as M&S in Beckenham) that offer a limited free period of parking operate this system. It makes sense when you think about it. How is the parking warden supposed to know when you arrived and if you are still within your free period if you don't get a time-stamped ticket?

Some of the misunderstanding in this particular car park might arise if people think the car park belongs to Sainsburys, which would normally be free.