Probably in connection with some sort of planned engineering work over the Christmas/Boxing Day shutdown Colas Rail's DR73923 heads south past Victoria bridge near Roade on Christmas Eve with the 10.10 Dorridge to Tring working. I have photographed this particular Plasser & Theurer switch and crossing tamper a number of times locally, for example......
https://www.ontheupfast.com/p/21936chg/29965829804/colas-rail-ballast-regulator-dr73923.