In a recent post, Librarian_Meets_Horse discusses his fence judge debut. While Mr. H is a newly-minted rider, from what I have read, folks in the UK will fence judge as a hobby without any interest in climbing aboard a horse. Ditto spectators.
This matches with a conversation fragment I overheard at Rolex one year. I was walking back from some briefing or another behind two big-noise officials. British Official asked what percent of the spectators were riders. American Official said almost all, most of them eventers. I would have added a few non-riding Lexington locals, but otherwise yes. This appeared to come as astounding surprise to British Official.
Two questions for Brits or British residents:
Is Eventing more of spectator sport in the UK than in the US?
What was the little yellow timer for?
Virtual Brush Box 
Lots of spectator-nonriders in UK. Badminton pulls in about 250,000 paid (yes, paid) spectators on cross-country day. A lot of them are just there to watch the pretty horses. Some are Pony Club, some foxhunters, but a huge minority just out for a day in the country with mud and excitement. And you should see the turf after 250,000 (and yes, that’s a verified count) pairs of wellies have tramped across it in the mud.