That is the first Mezzolitre chassis, and an early shot at that, so I'd guess from the clothes August 1951. I'd guess that it's the first test from all the faces, probably an old airfield South of Birmingham?
Second from the right looks a bit like Gordon Bashford, chief engineer at Rover, and who assisted on the design of the Mezzolitre. And I have half an idea the one in the middle is local hotelier Jimmy Byrnes. There's probably quite a few important players around as well, including the first two drivers Rupert Instone and Olaf Poppe (the latter played a key part in the creation of the Land Rover). Do you have any details on who's who?
<<< link removed >>>