I went on track at ford fair a few years ago, it was a novice session early in the day, had the briefing all about how you cant overtake a car unless outside of a corner, or on the straights they put an indicator on to let you pass. We were told quite sternly that if you overtake outside these rules you would be black flagged and removed from the track.
I spent the entire time stuck behind a bloke in a TVR thing who wouldn't let me past, which sort of ruined it for me, whilst plenty of other cars flew past us whenever they liked. Nobody was black flagged, nobody gave a shit. The rules are pointless because nobody enforces them.