In the U.S. I usually hear the phrase as “on the honor code” or “on the honor system.”
Here’s an improbable story (but entirely true).
I kind of assume – but I don’t know – that the London to Brighton Veteran Car Run is internationally famous, if only because it’s such a Goddam British Thing To Do. In case I’m wrong, a very brief intro: to celebrate the repeal of the Red Flag Act (and other restrictions on the newly invented Motor Car) an annual run for motorists was introduced in 1897, which rapidly became the London to Brighton run. The current rules limit entry to vehicles manufactured before 1 Jan 1905.The run takes place on the first Sunday of November.
There were just shy of 500 “official” vehicles in the run this year (including a handful of bicycles), plus trailers, support vehicles, people leaning out of car windows taking photos and video and – because this is all on open public roads – anyone else who has an old/classic car and who fancied taking part.
If you live between London and Brighton – which we do – the run is one of the milestone events of the year. We generally go and take a look, because that’s what you do. The precise route changes year to year, so sometimes we’ll just stroll out to take a look; another year it might be a brief drive. This year the changed route took the run…. right past our house. No shit, I could watch an internationally famous spectacle from my bed (!) Cool, huh? Doable, but not very practical.
I’ll post some photos from outside our house (literally, I was almost leaning on the fence) in a moment. In the meantime, here’s a short video that someone loaded earlier today, which gives a pretty good impression of what it’s like.
Side note for film buffs: Genevieve, as in the 1953 movie, is a real car and takes part in the run – we managed to spot her this year.
j
As promised
Steam powered:
This one was taken just down the road (we had to buy some milk!)
j
ETA: as always, click thru for the full image
That is the Goddam coolest British thing I’ve ever seen, @Treppenwitz ! It’s beautiful 
Carson Pickett - Wikipedia is currently on my super cool list.
Facebook Here she is with a little girl.