The PRORAIL UK website is currently undergoing redevelopment.
This site provides access to a substantial photographic and reference facility of worldwide transport interest. Of special note is the showcase offered for the railway photographs of the late A.E. "Dusty" Durrant.
The Prorail UK Photographic Archives
Some of the lists and representative images are already available but more content and information is being added on a regular basis. See current lists here