Not a Formula one race day. It's a motorbike race day. You can see a truck with Ducati on the roof.
Formula one is driven on Silverstone and not Brands Hatch.
You sound much more knowledgable about it than I am. However, there are a pair of what I think are Formula-1 chasis in a hospitality tent that led me to believe this was an F-1 Race. Here's the map:
To your credit there are a large number of motorcycles around the parking area, and it is odd that more car chasis aren't visible than the ones I listed above. Epsecially in front of the team trucks.
Raceways - Car, People 
Formula one is driven on Silverstone and not Brands Hatch.
http://virtualglobetrotting.com/map/16142/