That is interesting - I know pumps are calibrated and checked (by Trading Standards I recall?), but how often? One would think that most pumps are modern and sophisticated enough not to go out of whack at all...
Depends how bent the owner is...
http://news.bbc.co.uk/1/hi/england/wiltshire/4320774.stm
FWIW that charming gentleman is currently selling diesel at 133.9p/litre