Years ago it used to be normal practice when coming up behind someone you wanted to get past, to give a quick non aggressive flash of the headlights, and more often than not they would move out of the way to let you past.
Do that these days, and someone might just force you off the road and stab you.
Many years ago I was travelling up the chalk hills on the M40 when I came up behind a Vauxhall Senator in lane 3. It sat in lane 3 for some time so as I approached I gave a quick flash of my headlights. The Senator moved in to lane 2 so as I passed it I gave a two tone horn thank you and raised my hand as I passed. He responded with a two tone horn acknowledgment…… except his horns were a Police siren.
He did pull me over and thankfully he was an old school copper who just gave me a lecture and a warning about my speed, but with a grin on his face.
As we parted, he said “If sir would please accelerate hard on the hard shoulder before rejoining the motorway that would be good, but given the way you drive that shouldn’t be a problem to you”.
I’ll never forget that, and what a decent chap.