There were certainly no bare bottomed slipperings at the schools I attended. You did get boys showing off the slipper marks on their bottoms in the changing rooms after a PE lesson, I’m sure I did this myself once.
A Slippering was not considered to be a major type of punishment and after the initial pain could be quickly laughed off. I recall being very surprised at how painful my first slippering was and I was told how red in the face I was. You had only very thin shorts probably of the shiny type and of course, if you bent over the shorts became very tight. This was in the late ’60s and just a few years earlier PE kit for boys was quite different with thick baggy shorts as opposed to the thin tight ones we had to wear.