The additional shots particularly of Whirwind XJ726 clinch it for me as Halfpenny Green August 1971. Other notables present at that meeting included Gemini LZG, Provost WPH and Taylor Monoplane PRT. I am intrigued: how is it that behind the Whirlwind there is a group of people sitting on chairs around a table, not only out on the grass but also in the middle of a taxying area? My best guess is that it is a group of race officials situated where they can get a good view of the finish.