It is now being headed by New Zealand Judge, Justice Lowell Goddard. The Archbishop of Canterbury, Justin Welby, had asked Justice Goddard to investigate the Church of England first, saying that he would order his own inquiry if there was a lengthy delay.

On Friday, Justice Goddard announced that "the Anglican Church" would be the focus of one of 12 opening investigations of her inquiry. "I welcomed the invitation of the Archbishop of Canterbury for the Inquiry to investigate, as a matter of priority, the sexual abuse of children within the Church of England," she said.

"Our investigation will assess the appropriateness of safeguarding and child protection policies and practices in the Church of England and the Church in Wales. We will consider the adequacy of the Past Cases Review of the Church of England and the Historic Cases Review of the Church in Wales.

"As a case study, we will consider the experience of the Diocese of Chichester, a diocese that has been beset by allegations of sexual abuse, and subject to numerous investigations, reviews and inquiries.

"We will also consider the case of former Bishop of Lewes and subsequently Bishop of Gloucester, Peter Ball, and investigate whether there were inappropriate attempts by people of prominence to interfere in the criminal justice process after he was first accused of child sexual offences."

A timetable for each of the 12 investigations will be published in the New Year and public hearings are expecting to begin in February. The full inquiry is expected to last around five years.

Welcoming Friday's announcement, the Church of England reminded journalists of a speech given in the House of Lords in July by the C of E's lead bishop on safeguarding, the Bishop of Durham Paul Butler, who said: "I know [the inquiry] will take time and will be costly to undertake, and I know that for both those reasons it will be argued against.

"However, I firmly believe that the true cost of child abuse and the abuse of adults at risk is far higher than any of us have ever been prepared to acknowledge in terms of the mental, emotional, social and physical health and well-being of very large numbers of our population."

The inquiry will also investigate the Roman Catholic Church. "The sexual abuse of children within the Roman Catholic Church has been a matter of national and international concern for many years," Justice Goddard said. "The Archbishop of Westminster's calls for this Inquiry to be established reflected that concern. We will consider the extent to which [previous internal reviews] improved safeguarding and child protection policy within the Church and we will examine whether policy is effectively implemented in practice.

"In conducting the investigation, we will identify specific case studies, the first being the English Benedictine Congregation which has been the subject of a number of investigations and inquiries into child sexual abuse at schools run by the Congregation. The Inquiry will examine the relationship between Orders such as the Benedictines and the Catholic Church in England and Wales and will consider how that relationship impacts on child protection. In this way the Inquiry will evaluate whether any failings identified within the English Benedictine Congregation, and within any other case studies identified as part of the investigation, are representative of wider failings within the Catholic Church."

The other opening investigations will explore cases involving children in the care of Lambeth and Nottinghamshire councils, Cambridge House, Knowl View and Rochdale Council; the sexual abuse of children in custodial institutions and residential schools; the internet and child sexual abuse; child exploitation by organised networks; the protection of children outside the UK; accountability and reparations for victims and survivors; and allegations of child sexual abuse linked to Westminster.

The last of those inquiries "will focus on high profile allegations of child sexual abuse involving current or former Members of Parliament, senior civil servants, government advisers, and members of the intelligence and security agencies," Justice Goddard said. "It will consider allegations of cover-up and conspiracy and will review the adequacy of law enforcement responses to these allegations."

The investigation into the churches will be headed by Professor Malcolm Evans from the University of Bristol, an expert in international law, particularly in areas of the law of the sea and religious liberty; human rights and the prevention of torture.

In making Friday's announcement, Justice Goddard acknowledged that the Inquiry could take some time to complete. "It is impossible to put a timescale on the completion of all of this work, but it is reasonable to assume that while some of the investigations may be completed within 18 months, others may take several years to conclude," she said. "In some cases, overlapping criminal proceedings may cause substantial delay to the progress of individual investigations. Nonetheless, in my opening statement I committed to completing the work of the Inquiry within five years and my current assessment is that that timeframe, whilst ambitious, is achievable."

Welcoming Friday's announcement, the Victims and Survivors Consultative Panel to the Inquiry said in a statement: "Too many victims and survivors of child sexual abuse have suffered in silence. These investigations will give public voice to that suffering and bring greater understanding of why so many horrific crimes went unreported and undetected for so long.

"They will enable the Inquiry to make proposals for reforms that will better protect children in the future and improve the support and reparation available to victims and survivors."