Explanation

"At junctions controlled by traffic lights, you must stop and wait behind the white line until the lights change to green. You may then proceed unless your exit road is blocked or it's not safe to do so, such as when pedestrians are crossing in front of you. After the green light, the amber light will show on its own for a short period, followed by the red light. When the amber light shows on its own, you should stop, providing it's safe to do so."