It's a small world !!!
From the first image of the train passing West Hoathly, I believe that is me pictured in the brake van. From Horsted Keynes to Kingscote the train was hauled by the engine. At Kingscote the engine runs round, to enable the formation to be propelled up the northern extension to the railhead. The northern extension is a siding under an Engineers' Possession. The return journey back to Horsted Keynes is hauled by the engine as per your photo.
You will find several pictures of various engineering trains in my collection here >>>
http://gallery74781.fotopic.net/c437580_1.html
Chris (Passenger/Goods Guard)