Funny...similar thing happened to me today...on the M1 coming back from Chesterfield.
a white Rover full of "Chavs"...Oldest about 18 years if a day.
Playing "chicken", swerving backwards and forwards inbetween far left and far right lanes...Frightening the Little old ladies and making them swerve, squeezing inbetween lorries etc etc etc.
I'm afraid I just sat back and made sure that my kids and I were as far away from them as possible...
I'm sure that the well placed cameras would have spotted what was going on...Well I hope they did.