Not all teachers approved of corporal punishment. There were at least two who were adamantly opposed to it, and there may well have been others.
The school’s most senior teacher had a history, going back twenty years at the time I was at the school of stepping in any case where he felt the strap was even coming close to being misused. He used the strap himself on occasion, but only in cases that were very clearly in line with policy. I have absolutely no doubt whatsoever that he would have taken action if he saw a hint that a fellow staff member was acting inappropriately – because he had done so, even as a relatively junior member of staff – and by my time at the school, he was a very senior member.