You can take photographs at stations provided you do not sell them. However, you are not allowed to take photographs of security related equipment, such as CCTV cameras.
Flash photography on platforms is not allowed at any time. It can distract train drivers & train despatch staff and so is potentially very dangerous.
Tripod legs must be kept away from platform edges and behind the yellow lines. On busy stations, you may not be allowed to use a tripod because it could be a dangerous obstruction to passengers.