A. When the other vehicle signals to overtake
B. As soon as the other vehicle moves out to overtake
C. As soon as the other vehicle passes you
D. After the other vehicle pulls in front of you
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When you are being overtaken, dip your headlight as the other driver comes past so that you don't dazzle them in their rear view mirror.
If you are the one overtaking your lights should be on dipped beam. It's permissible to give a quick flash of your headlights before you start the overtaking manoeuvre to warn the driver ahead. Don't put your lights on full beam until you are past the level of the driver of the vehicle you're overtaking.
If the driver of the vehicle you're overtaking forgets to dip their headlights, adjust your rear-view mirror to avoid being dazzled.
The Highway Code Rule 115 says:
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