Sexual abuse at two British Catholic schools over four decades was likely to be "considerably" more widespread than conviction figures reflect, a report has found.
Monks at Ampleforth in north Yorkshire and Downside in Somerset hid allegations of "appalling sexual abuse" against pupils as young as seven to protect the church's reputation.
The Independent Inquiry into Child Sexual Abuse (IICSA) made the claims in an report on the English Benedictine Congregation, which has ten monasteries in England and Wales.
Ampleforth and Downside are two schools linked to the monasteries, run at times by "secretive, evasive and suspicious" church officials who avoided reporting misconduct to police and social services.
Allegations stretching back to the 1960s encompassed "a wide spectrum of physical abuse, much of which had sadistic and sexual overtones", according to the report.
Ten individuals linked to the schools, mainly monks, have been cautioned or convicted over sexual activity or pornography offences involving a "large number of children".
"The true scale of the abuse however is likely to be considerably higher," the investigation, led by Professor Alexis Jay, found.
The report followed several weeks of evidence hearings at the inquiry last year, which included personal accounts from victims.
Victims were as young as 11 at Downside and seven at Ampleforth.
One alleged offender at Ampleforth abused at least 11 children aged between eight and 12 over a "sustained period of time", but died before police could investigate.
"Many perpetrators did not hide their sexual interests from the children," the report found, allowing abusers at Ampleforth to prey on entire groups of pupils both outdoors and indoors.
"The blatant openness of these activities demonstrates there was a culture of acceptance of abusive behaviour," the report said.
This was a culture fostered by the abbot leading the schools, it was claimed.
In 2001, the Nolan Report recommended all sexual abuse allegations within the church must be referred to police, a position which many felt was "neither obligatory nor desirable".
Child protection issues were not limited to the distant past, the report found.
In 2016 and 2017, former abbot of Downside Aidan Bellenger sent two letters to Dom Leo Maidlow Davis, highlighting how four suspected paedophiles remained at Downside, but this information was not passed on to the local authority safeguarding lead.
Dom Leo eventually apologised, but the report said: "The whole incident, having occurred so recently, gives no cause for confidence that the attitudes at Downside had changed enough to put children first over threat to reputation and embarrassment to senior members of the monastic order,"
The congregation's most senior clergymen including past presidents Dom Richard Yeo and Dom Charles Fitzgerald-Lombard refused to fully accept that criminal activity was tolerated when questioned at the inquiry.
The Catholic Church is one of 13 strands of public life being investigated for child protection failings by the IICSA.
Ampleforth School said in a statement: "We have publicly accepted responsibility for past failings on many occasions, and the Ampleforth of today has never been afraid to learn difficult lessons.
"We would like to thank Prof Jay and her team for the hard work that has gone into this comprehensive and extensive report and we will review it to identify anything that could inform our constant drive for improvement.
"In the meantime, we remain completely focused on the safety and wellbeing of those entrusted to our care and our commitment to implement meaningful change".
It ended: "We would also like to once again offer our heartfelt apology to anyone who suffered abuse while in the care of our schools, parishes or other ministries".
