10/20 . 1921,
Sorry, make that 1922, I've just found a similar image on "lost marques" website. Interestingly, the site has two photos of Enfield-Allday cars which took part in 1922, and they are totally different. One in numbered 73 (very unlikely number for that race), and has a high chassis and looks more like a sports version of the standard car. That's what made me state earlier that the puzzle couldn't be an E-A car. The other image is very similar indeed to the puzzle, minus the racing numbers.s