That did cross my mind. So that would've been an RV with Oscar's Dad and the Essex contingent either by the Tilbury Ferry or the Promenade cafe in Gravesend, followed by a ride to the Horseshoe & Castle in Cooling, and then an escorted ride along the Thames path to the camping site at Crystal Palace.
If it is that, I still cannot figure at which point we would've been as close as your pic shows to a container port ???
Unless, of course, you were using The Very Special Lens. Like f 0.001. Or summat.
And I don't recognise the riders dressed in red.