Like you I was rarely on the receiving end. Only twice in fact, the first of them in what in most schools would have been the top class of Infants, but for some reason (most probably, on reflection, the building layout) my schools operated a three form Junior school, so there it was the next to the top Infants class. That was the leg smacking, and it made me resolve to avoid CP thereafter, an objective in which I was pretty successful!
But though I dodged it myself, an awful lot of classroom CP went on, mostly in the Junior school. However I don’t recall anyone ever being sent to the Headmaster (though he caned pupils from the associated Senior school, of which he was also Head). In the Junior school both boys and girls were smacked, rulered and slippered by a variety of techniques, both in lessons and at the end of lessons. Usually the former, as for the most part one teacher taught one class all the time, so there was no point in waiting to administer a punishment.