Yes, I do know the washing line protocol, but suspect it differs from one part of the UK to another.
One of the (many) things that went wrong between my Grannie (Daddy's mum) and my mother, was that as a very new, foreign daughter in law my mother hung her own and Daddy's underpants on the same clothes line, while they were living with my grandparents. Grannie flipped out over the sheer indecency of men and women's undies on the same line, and my mother, by her own admission, made things worse by saying that as she and Daddy were married, she supposed their underwear was too!
I was taught to peg shirts, blouses and t-shirts in the arm-pit so the peg marks didn't show, that everything that could be expected to dry at the same speed should be hung together, for ease in taking it in, woollens in the shade, bras and suspender belts where they could not be seen from the street and that underpants should be hung by the waistband. My maternal aunt hung hers by the crotch, apparently finding that more decent. Nothing my childhood home had to be hidden, but I had a college friend whose mother always covered her underpants with a towel or hung them inside a pillow-slip. I do tend to hang black lace panties and other frivolous items where they can't be seen on the back lines of the rotary drier, as I do not see that my husband and my private taste concerns the neighbours.