An Observer Magazine investigation has uncovered a series of alleged sexual assaults at Aberlour House, the junior school of Gordonstoun, the Scottish public school where the Queen’s sons were educated. In one of the most shocking cases, a victim has told how she was raped in a tent by a teacher on a school camping trip while other children listened. She was just 12.

“Kate”, a scholarship pupil who has never spoken out before, said her life was “smashed up for a second time” when the sexual assault trial she had prepared herself for collapsed after another witness withdrew for personal reasons. The Observer has been told by legal sources that if the case had been in England, the prosecution would have gone ahead.

“I was looking forward to it, even though it would be horrendous,” Kate said. “I knew I’d be a blubbering mess in court, but I wanted it, and now it was taken away … I still don’t know how to move forward.”

After the alleged rape in 1990, Kate – and another pupil who also claims she was raped by the same man – went on to Gordonstoun’s senior school. Kate says she suffered years of bullying and abuse as a result of the camping trip incident. The bullying stopped only when she was 16, after her father was killed in an accident and she tried to kill herself.

Kate decided to report the crime in 2013, after a group of more than 100 former Gordonstoun pupils started a Facebook campaign to get the school to recognise the historical problems it had with bullying, abuse and inadequate child protection.

Gordonstoun says it has made contact with the group of former pupils, “expressing deep concern for everyone affected, and encouraging anyone with evidence of criminal behaviour to contact the police, and promising to provide support for those who wanted it”.

A Gordonstoun spokeswoman said the school had co-operated fully with the police in the past and would do so in the future if necessary. She added: “Child protection is something we take very seriously and we are committed to providing a safe and nurturing environment for all our students.”

Scottish police arrested Kate’s alleged attacker and he made a first court appearance in 2013. But an attempt to bring a prosecution collapsed last autumn because of a much-criticised Scottish law that demands a second witness to corroborate crimes, even those committed in private.

In another incident investigated by the Observer, a 12-year-old boy, John, was assaulted in his dormitory at Aberlour House by an English teacher named Derek Jones. That case was reported to the police, but Gordonstoun gave a “cast-iron guarantee” that if John’s parents gave up a prosecution they would make sure Jones never taught again.

Last year John, now 37, decided to seek justice. It turned out that, after being sacked, Jones did teach again: he went on to offend at an English school and possibly one in Kenya. He died there five years ago in a car crash.

Scotland’s “corroboration” law is widely blamed for the fact that so few reported sexual assaults or domestic violence incidents in the country lead to prosecutions. In recent years only 9-12% of rape reports have ended in prosecutions compared with about 20% in England. In 2013-14 in Scotland, 1,808 rapes or attempted rapes were reported to the police. There were 214 prosecutions, and just 87 convictions – one of the lowest report-to-conviction rates in Europe.

Rape Crisis Scotland (RCS) explains the convoluted procedure north of the border. “In a rape case you need two forms of evidence that penetration took place, two forms of evidence that there was no consent, two forms of evidence that the accused knew there was no consent and acted with malintent, and two forms of evidence that it was the accused who committed the crime,” said an RCS spokesman.

“This alleged case [at Gordonstoun] shows, once again, the urgent need for Scottish law to be adapted to address the reality of sexual crime and to improve access to justice.”

According to figures released by the Crown Office in Scotland, 60% of complaints of domestic abuse go no further, because of corroboration requirements.

Scotland also differs from England in that it does not permit pre-recorded video evidence in court, though this can help vulnerable or frightened witnesses to come forward, and would have assisted in Kate’s case.

Meanwhile, people like John, whose abuser has died, are prevented from suing for compensation because the crime occurred so long ago, a rule that has been lifted in civil courts in England for victims of historical abuse.

Last year an attempt by the SNP, backed by police and prosecutors, to reform the law on evidence in Scotland was derailed by concerted lobbying from much of the legal establishment. However, a committee, headed by Lord Bonomy, set up to investigate corroboration and other anomalies in Scottish criminal law, will issue a report and recommendations later this month. Campaigners hope these may include an end to the corroborating witness demand in sexual assault and to Scotland’s three verdicts – guilty, not guilty or “not proven”.