Scores on the door are actually useless.
For one they're assessed every year.
So a fabulous restaraunt can get a 2 or 3 due to structural issues and lack of confidence in management (if the general manager is off sick and a team leader stands in but doesn't know exactly how to answer the inspectors questions 100%).
But a shit restaraunt can have a good day, too. Leading to the opposite happening.
The worst place I ever worked at for food safety was a 5/5. Mold in the pot wash, chefs handling raw chicken then handling cooked rice balls and serving them like that...
Seriously a score on the door means fuck all - even if the initial score was accurate a month later there may be new chefs, managers or an owner which can completely change everything but the rating will stay the same for 11 months...
Also, no ones going to do anything bad (ie spitting in food serving out of date food handling raw meat then cooked food etc) in front of a council inspector are they!
I don't know why people take so much stock in these things...
as for the worst things I've seen...
a customer spunking in buffet mashed potato. He then went to other pubs in the area and did similar. Was arrested the next day.
A chef serving incorrectly defrosted meat, leading to severe illness and killing one person.
A kitchen that was so filthy you could get a spoon, scrape the surface and it still wouldn't be white (the colour it was meant to be!) it took 2 chefs 2 bar staff and a manager to get the place service ready, in 12 hours. I'd taken the job there and refused to work until it was at an acceptable standard.
source: chef for over a decade....