What action should be taken upon hearing one long whistle from the tower?

Upon hearing one long whistle from the tower, the appropriate action is to stop all movement immediately within interlocking limits. This signal typically serves as an indication of a critical condition or warning. Stopping ensures the safety of both the train and its operations within the area, allowing time to assess the situation before proceeding.

While some other responses might suggest continuing movement or exercising caution, these actions could lead to unsafe circumstances if the warning signifies a potential hazard or a need for immediate cessation of operations. Proper adherence to this signal is crucial for maintaining safety standards on the railway.