The Highway Code advises that a green traffic light means:
Go
You can proceed if way is clear
Proceed with extreme caution
You have priority over pedestrians
You are in the red car (Car A), and want to go straight ahead at the traffic lights. You have accidentally selected the wrong lane with a green filter arrow. Which of the of the following actions will you take:
Carry on to the left and turn around later to return to your intended direction?
Wait for the main green light to show and then drive on ahead?
Cross the stop line to move into the clear space (C) in front of car B until the green light shows?
You must stop at a steady amber traffic light unless you are so close to the line that stopping might cause an accident.
At temporary road works traffic light you:
Must always wait for a green light before proceeding.
Can proceed at a red light if you can see that there is no traffic coming from the opposite direction.
Can proceed at a red light if you can see if a driver from the opposite direction flashes their headlights, indicating that their light has turned red.
Can proceed at a red light if the road is clear and there are no workmen on site - for example, at night.
This police signal means:
Traffic approaching from both front and behind must stop.
Approaching drivers must stop and then turn right.
The officer is diverting traffic to the right. It's not necessary to stop.