Thanks for the point, Pal, but I hadn't really completed the puzzle. I wasn't sure from an earlier reply if this was the 1931 Cape Town expedition or not, and wanted to check if I had the right person first!
As you say, Captain Geoffrey H. Malins was an official cinematographer in WW1, and made two particularly well-known films, called "Battle of the Somme" (currently available on DVD) and "Battle of the Tanks".
Another claim to fame was that in 1926 he set off with a colleague to travel round the world by motorcycle. He wrote a book about this called "Going Further", published 1931.
And for another snippet about the London to Cape Town expedition, as the Rileys were expected to have to cross rivers, they were equipped with inflatable pontoons for buoyancy, so that they didn't have to rely on bridges. I don't think the design was fully thought through, though, as the fixing racks made it impossible to steer the cars with the pontoons fitted, so they couldn't be driven on land without removing them.
