Generally none. They’ll have a look around and see if anyone is using the machines or walking between the car and the machines. If not, they’ll issue a penalty.
The moment you walk off and either leave the car park or disappear round a corner into another street, you’re fair game.
Walking away to get change from a shop, and things like that, generally aren’t allowed. Walking out of an underground car park to get better mobile signal is somewhat OK.
Generally if you paid within two or three minutes of getting a PCN, you’ve got an OK appeal. More than five is tough unless you’ve got a very good reason.
