While watching a documentary film on TV channel 73 about the 1953 German Grand Prix, I noticed these parking area scenes (still captures below).  My first thought was to wonder what involvement the Rootes Group had in open wheeler racing.  They were heavily involved in rallying from the late 1940s.  The name Stirling Moss on the front of the Commer transporter also had me wondering.  He was a prominent Grand Prix racer at the time (he finished 6th in this race), but not with the Rootes Group.

The Wikipedia page for Stirling Moss concentrates on his Grand Prix career, but there's a passing reference to him being "also a competent rally driver" and "he finished second in the 1952 Monte Carlo Rally driving a Sunbeam-Talbot 90 with co-driver John Cooper."

In March 1953, the new Sunbeam Alpine sports tourer was released.  Rootes Competition Department built a set of 6 special works cars.  Stirling Moss finished 14th in 1953 Monte Carlo Rally, then won it 1954.  In the 2nd picture above (on 2nd August 1953), near the rear of the Commer transporter, you can see the front of what is presumably an Alpine (or perhaps a slightly older Sunbeam-Talbot 90) to be run in a support race.  Stirling Moss, like many of his contemporaries, raced several cars in different classes during a race meeting.

A bit more history about these Sunbeam Alpine Mk. I competition cars: http://www.bonhams.com/auctions/20145/lot/157/

Two relevant chapters in the 2008 book "Rootes Maestros" by Graham Robson –
  * Stirling Moss: A reminiscence of the 1952 Monte Carlo Rally
  * Humber Super Snipe: The Fifteen Countries in 90 Hours run

This photo caption indicates that Moss & Johnson were set a target of 5 days (120 hours) for their 15 countries run in the Humber.