The Riley on the left appears to be the 12/4 Army Tourer prototype, and has a Coventry early summer '36 registration. The other is allegedly a Humber, but could be a Hillman. I suspected that it's a '36 Humber 6-seater Tourer with Hillman radiator, but now wonder if it was a Hillman Hawk. Two Hawks were trialled, one with 9.00 x 13 tyres, the other 6.00 x 16 tyres. Any ideas please? The photo is at Alt-y-Bady I think in Snowdonia, Wales, autumn 1936 and blinking chilly! Oh! The 1936 War Department Trials.
http://www.chrishodgephotos.co.uk/pixcma2/04183.jpg