Showing a white light to the rear, in the UK, is an offence, but if I'm tailgated at night with headlights blazing in my mirrors, I dip the interior mirror, then raise the electrically adjustable door mirrors till they reflect the bastard's own lights straight in his eyes. I'm not showing a white light, he is. I'm simply adjusting to avoid being dazzled

It doesn't matter if he stays behind or pulls left or right, he can't get out of the beam.

It never takes more than about twenty seconds before he drops back to a safe distance.

In daytime I just slow gently till he's forced to overtake.