I read an answer on another site which referred to the idiom of falling off the wagon as being "chiefly American". That got me curious since I would have thought that this particular idiom is shared by both sides of the pond. I tried an NGram of fall off vs drive the wagon, and could find hits on both their BrE and their AmE corpus, but of course that isn't really conclusive as there's no way to compare. There is a hint though as I noticed that there is a clear hike in usage in BrE in the past few years (after 2000), so that could indicate that it used to be less common in BrE.
This makes sense since the idiom itself is attested from 1904, but it apparently arose in the US during prohibition, so it likely was indeed more common in the US at the turn of the century. Is that still the case today? Can we still say this is "chiefly" an AmE expression or is it now simply an English language one understood and used in both AmE and BrE (and others, presumably) equally?
Updating here to incorporate my comment below:
I am not distinguishing between [to be] on the wagon and falling off the wagon, I'm asking if the general idiom of the wagon meaning abstaining from alcohol, be one on it or off it, is more common on either side of the pond today.