There is no time frame on the national child abuse inquiry because new forms are emerging all the time, its chairwoman has said, adding that its vast scale is a "virtue".
The Independent Inquiry into Child Sexual Abuse (IICSA) intends to produce an interim report by March 2018, Professor Alexis Jay said, speaking after the publication of her review into the troubled inquiry.
Due to "new and emerging forms of child sexual abuse... it may be necessary to open other investigations" increasing its length, she added.
Prof Jay said by 2020 the inquiry intended to have made "substantial progress", but she could not give an end date because "we don't know what we are going to find".
The inquiry, which began in 2014 has cost £23.6 million to date, but Prof Jay said she has made no attempts to streamline it since taking charge, because its "scale is a virtue" with a "great deal of transferable learning".
This "transferable learning" is "actually very helpful in speeding the inquiry up", and as a result the size and scope of the inquiry "remains unaltered", the former social worker added.
Former chair of the inquiry, Dame Lowell Goddard had called for the inquiry to be pared back, saying there was an "inherent problem" in its "sheer scale and size".
Prof Jay explained: "It is extremely important that victims and survivors have the opportunity across a range of institutions to tell us about their experiences and for us to question these institutions about their responses to child sexual abuse."
The large scale of the inquiry allowed those working on it to "see patterns in behaviour which are actually very helpful in speeding the inquiry up".
Currently the inquiry is investigating 13 different strands spanning several decades and examining a host of different institutions are currently being pursued.
The 67-year-old said she "hoped" it would not take 10 years to be complete.
Prof Jay said the review into the inquiry had not been set up to make it less bloated, but to "give some clear sense of direction and purpose to it".
In the future the inquiry would try to be more clear about its work and the timescale it intended to achieve it in, Prof Jay added.
Due to the advancing age of some of the survivors and victims, certain aspects of the report - such as looking into the child migrant programmes which took place between 1920 and 1960 and saw 150,000 "orphans" despatched abroad to Australia and Canada - were being looked into first.
Prof Jay said her controversial decision to postponed the investigation into Lord Janner had been made due to the ongoing Independent Police Complaints Commission (IPCC) inquiry.
She said she did not want to "replicate" work already done, "contaminate any evidence" the IPCC may be looking at, and "put victims and survivors through multiple experiences of interviewing, because for many that very experience can re-traumatise them."
Giving an update on the Janner strand, Prof Jay said it would have a stronger focus on institutions and it may not be necessary for a "finding of fact" to be made on the truth or otherwise of a specific allegation of child sexual abuse.
Janner, who died last year, faced a string of allegations that he abused young boys in the 1960s, 1970s and 1980s.
The child abuse inquiry's investigation into him will not take place until 2018, having originally been intended to start in spring 2017.
In November the inquiry came under fire after allegations of bullying and sexual assault at its headquarters were found to have not been taken seriously enough and the inquiry's response to these claims were "inadequate", a Commons report claimed.
What is more, Ben Emmerson QC, the most senior lawyer appointed to the inquiry resigned in September, following an allegation he had sexually assaulted a female "inquiry worker" in the lift at its offices. Mr Emmerson strenuously denied the claim.
A replacement for Mr Emmerson is expected to be announced soon.
While in November, another senior lawyer in the inquiry, Aileen McColgan, reportedly resigned.
Prof Jay's review also found:
The strategic approach of the inquiry, delivering through three major strands of work - public hearings, research and analysis, and the Truth Project - is right, but its implementation has been too slow.
The inquiry has done valuable work in a number of areas, but must demonstrate this more clearly.
The inquiry should publish a regular timetable of its activity starting in 2017/2018.
The inquiry's work needs "rebalancing" to make sure sufficient attention was paid to making recommendations for the future.
The inquiry's commitment to exposing past failures of institutions to protect children from sexual abuse should remain unchanged.
Sets out measures to accelerate the progress of public hearings, with four planned for next year.
The governance of the inquiry needs revising to provide stronger accountability and oversight of the programme of work.
Reveals that legal requests have been sent to hundreds of institutions, while 86,000 documents have been received so far.
Those with an interest in the inquiry's work should have more opportunity to engage with it.
The inquiry's relationship with victims, survivors and others should be kept under constant review.
The inquiry also published updates on its investigations. They include:
Allegations of child sexual abuse linked to Westminster
The inquiry has requested and obtained documents and statements from political parties, individuals and the Home Office.
It has inspected documents held by the Cabinet Office and the security and intelligence agencies.
It expects to open the window for core participant applications in the third quarter of 2017, with a first preliminary hearing to follow.
Children in the care of Nottinghamshire councils
The inquiry has been analysing the material received to date, which amounts to around 600 documents.
It is currently considering whether it may be necessary to make some changes to the investigation's definition of scope, to ensure it remains "focused and proportionate".
The investigation into institutional responses to child sexual abuse and exploitation facilitated by the internet is expected to issue requests for evidence in early 2017, with the first public hearing in early 2018.
Child sexual abuse in the Anglican Church - Material is being analysed, with the first public hearing planned for March 2018.
Child sexual abuse in the Roman Catholic Church - Thousands of potentially relevant documents have been obtained, with a public hearing scheduled for December 2017.
Protection of children outside the UK - A first public hearing on child migration programmes case study will be held in February.