if a boy was abused while he was headmaster and he knew about it and took no action it would be sean as a gross derliction of his dutys so if it did happen i very much doubt he would want to mention it so i douvt if hes the source.
Part of me wonders why so much is being made of this alleged incident. Such things appear to be 'rites of passage' for some, in (boarding) schools world wide. Why did the Headmaster do nothing about it? We don't 'know' that there was anything to do something about and if there was it's unlikely, unless it was endemic and/or reported at the time, that the Headmaster ever got to hear of it.
Examining what Jeremy was like at the time, I think we're certainly likely to find the proverbial "fish out of water". From stories told of him during his time at Maldon Court, his prep school, he was said to be the scourge of the school bus, a regular and spiteful bully. If these stories are true, we see a Jeremy who was confident enough to feel he could get away with such behaviours. It's sad, if not cruel, that boarding school coincided with him learning of his adoption. It may have made him feel that he was a secret which couldn't be shared. I believe it would have changed him from a child who felt powerful and confident enough to bully others into one who was ripe for being bullied and I can only imagine the anger he must have felt at being rendered so powerless and helpless. It's unsurprising, then, that later in his school career, he once again gained the reputation of being a bully. I find it telling -and not a little disturbing- that few -ANY- of his peer group has come forward to speak about jolly times they enjoyed with him when they were children. Surely, had he been popular, they'd have fought tooth and nail to support and defend him?