Yesterday, the inquiry published a report into two independent schools connected to abbeys - Ampleforth College, run by the St Laurence Education Trust, which the commission opened a statutory inquiry into in 2016, and Downside College, which is also charity run.
The report found that 10 individuals, mostly monks, connected to the two institutions had been convicted or cautioned in relation to offences involving sexual activity with a large number of children, or offences concerning pornography.
But it says "the true scale of sexual abuse of children in the schools over more than 40 years is unknown", and was likely to be "considerably higher".
Both organisations "prioritised the monks’ and their own reputations over the protection of children" and when obliged to work with the authorities they "gave the appearance of cooperation and trust" while adopting a "’tell them nothing’ attitude", the report says.
At Ampleforth, the report said, abuse had taken place openly and involved "communal activities".
"The blatant openness of this behaviour demonstrates there was a culture of acceptance of abusive behaviour," the report says.
The commission opened an inquiry into the St Laurence Education Trust in November 2016 and appointed Emma Moody, a partner of the Newcastle law firm Womble Bond Dickinson as interim manager in April this year following concerns the charity had not made enough progress on implementing recommendations made by an independent review of safeguarding at the charity.
Michelle Russell, director of investigations, monitoring and enforcement at the commission, said the regulator has been very clear that safeguarding is a governance priority for all charities.
The commission had opened the inquiry because it was "not satisfied that the charity’s safeguarding policies, procedures and practices were adequate and working properly".
She said the findings and conclusions of the IICSA report about both organisations would "be taken into account for our own regulatory purposes as part of ongoing engagement with the charities".
In a statement, Ampleforth said it had publicly accepted responsibility for past failings and was now "completely focused on the safety and wellbeing of those entrusted to our care and our commitment to implement meaningful change".
It also said it was now working with Moody to develop a safeguarding charter, which it hoped would become recognised as best practice for safeguarding in education.
"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," the statement said.
A statement from Downside said it "fully acknowledges the serious failings and mistakes" it had made in protecting those in its care and responding to concerns.
"We would like to reiterate our sincere and unreserved apology to all victims and survivors of sexual abuse suffered as a result of the actions of some within the Downside community," it said.
It said significant changes had been implemented to raise safeguarding standards at the school in the past few months.