I disagree, it doesn't result at all in a "net increase" of lawfulness, it's just an extra person breaking the law and driving badly. UK highway code is pretty

I disagree, it doesn't result at all in a "net increase" of lawfulness, it's just an extra person breaking the law and driving badly. UK highway code is pretty clear on when it is acceptable or not to flash your headlights. Using them to alert others to your presence (ie, "I'm here please turn off your high beams") is fine. Doing it like the parent poster suggested could result in a £1000 fine if caught.