Officers from Police Scotland will travel to Newcastle tomorrow to interview Andrew Lavery, 41, who for two years in the 1980s attended the fee-paying Fort Augustus Abbey, which was run by Benedictine monks. "It was systematic, brutal, awful torture," says Lavery, who says he was beaten, sexually assaulted and isolated in a locked room for days on end under "special measures". He added: "The psychological torture was the most damaging. In the end I wanted to kill myself."

Lavery claims he was beaten unconscious by a monk and lay master while pupils watched, then left at the playing fields to crawl back to school. He also says he experienced "greying", which involved other pupils pinning the victim's legs apart while his testicles were hit with a hockey stick. A monk watched without intervening. "I have had pain in my left testicle all my life," he said.

Lavery also accuses Monk A, now a cleric in England, of physically beating and sexually assaulting him. He will tell police that when he broke his leg Monk A took advantage of his vulnerability and tried to grab his testicles. "I told him to leave me when I went to the toilet, but he was standing over me. He said, 'No, you need a hand.' I heard all his heavy breathing behind me. It was the wrong sort of breathing to hear in your life. He was fumbling and I was screaming at him to get off."

Monk A is also accused of selling alcohol to underage pupils. When contacted by the Observer, he admitted giving them beer, but said: "I never beat people up and there was certainly never any sexual stuff. I don't know what he's talking about."