Hear Hear Jonathan, that really pisses me off. I've got some disabled family and they don't always use the disabled bays if there is other parking close by - as they say there is always someone worse off than they are.
I've been threatened when asking a young guy to hang his permit on the dash in case people thought he was just using it as a 'convenient' park. For some reason people also don't like you taking a picture of their car, if it's got a company logo I send it on to them congratulating them for hiring disabled people and recommending they contact the local newspaper for a feature story.