Mr McLellan, who is also a former inspector of prisons, admitted he had been surprised to be asked to lead the commission and insisted he had not accepted the job as an "ecumenical adventure".

Speaking at a launch event in Edinburgh, he said: "I am not here representing the Church of Scotland but my own church has learned a lot about helping parishes to 'own' and to love safeguarding.

"That is part of the culture change, which the Catholic Church needs to learn as well."

The Kirk stalwart also suggested there were new teachings in the Presbyterian faith that could be applied to the Catholic Church which, under Pope Francis, is grappling like never before with historical issues of physical and sexual abuse.

Mr McLellan said: "We have done a fairly significant theological piece of work about balancing the responsibility of a Christian organisation to forgive against the responsibility of a Christian organisation to protect.

"We have tried to think that through. It has helped us to form policies in our church. And that kind of thinking is very important for the Catholic Church to do as well."

The former moderator stressed he did not expect the Catholic Church to simply copy the Church of Scotland.

He said: "I am hoping that they will themselves choose to change the culture and theology of their church.

"It will be unlikely that they will feel the Church of Scotland is the example they will follow. The process we have been engaged in encourages me to think that a church can change with regard to the protection of vulnerable people."

The McLellan Commission is not investigating individual cases of historic or current abuse. It does, however, want to hear from those who have been affected by such issues as it tries to make protection mechanisms more robust.

He said: "Although it is not within the scope of the Commission to investigate or adjudicate on current or historical allegations, we will listen to the experience of survivors of harm and abuse within the Church. It will draw on such experiences in identifying what aspects of the approach to safeguarding have helped or hindered matters being raised and addressed."

Mr McLellan said his Commission, which includes Police Scotland Assistant Chief Constable Malcolm Graham, would report any crime it became aware of to law enforcement authorities.

He said: "Our task is primarily to help to protect children and vulnerable adults. It is not to protect the Catholic Church. But we do want the church to get right its policies and practices with regard to abuse. The only credible policy for a church is 'no abuse, no cover-up'.

The Catholic Church itself is carrying out a "statistical review" of abuse cases dating back to 1947.

Mr McLellan declined to say if he believed his commission - or another independent body - should have done this work. That, he said, was a matter for the church.

Mr McLellan also defended the appointment to his commission of Stephen Robson, the Bishop of Dunkeld and a former colleague of Cardinal Keith O'Brien. Cardinal O'Brien stepped down last year after admitting inappropriate sexual behaviour. He said: "I don't believe my commission is inhibited by the precence of Catholics. I think this is a help."

The Commission is expected to report in 2015, after which the Church will consider ­ whether to implement any recommendations.