The shutter has been pressed very early but with the very limited fast shutter speed on the Exa camera of only 1/150th sec. if it had been any closer motion blur would have spoilt the image; I was thinking ahead! The image shows 46011 on an up PW working of some kind, probably heading towards Westbury. Apart from the train, this picture is full of interest. On the far right is the former up facing bay platform. Sitting above the down canopy is the remains of the former signal box that commanded a lofty position above the station giving good views in all directions. In the background is the tower of St. Mark's church. In 2014 I stood in s similar position and took a photograph of 158960 leaving the station, the scene is remarkably similar, see.....
https://www.ontheupfast.com/p/21936chg/29945957604/x1-158960-gw-14-30-cardiff-c-portsmouth