Chairwoman Professor Alexis Jay, who led the inquiry into child sexual exploitation in Rotherham, rejected suggestions that the remit of the probe was too broad to succeed - describing its scope as a “virtue”.
She said she plans to make recommendations in an interim report in 2018 and spoke of her determination to make “substantial progress” by 2020.
However, no final date has been given for what is the largest public inquiry ever established in the UK.
There have been suggestions that it could last for up to a decade.
Today, Professor Jay published a review of the troubled inquiry, which she announced in August after being named as its fourth head since it was launched in 2014.
Thirteen different investigative strands spanning several decades and examining a host of different institutions are currently being pursued.
There have been calls for the inquiry to be pared back, with former chair Dame Lowell Goddard saying there was an “inherent problem” in its “sheer scale and size”.
However, a report setting out the findings of the review said the inquiry remains committed to pursuing each of the existing investigations as they play an “important part” in its task of examining institutional failure.
Prof Jay said: “There have been suggestions that the remit of the inquiry is too broad to succeed. I disagree. Its scope is a virtue, allowing it to recommend fundamental changes beyond the reach of an inquiry with a narrower remit.”
The inquiry is proposing changes to the scope and timing of the public hearing for the investigation into the institutional responses to allegations of sexual abuse involving the late Lord Janner of Braunstone.
In the Janner strand there will be a stronger focus on the 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, according to a provisional determination published by the inquiry.
Submissions on the proposals are being sought before a final decision is taken, with “substantive” public hearings in the investigation unlikely to be held before 2018.
Lord Janner, who died in December, is alleged to have abused youngsters over a period spanning more than 30 years dating back to the 1950s. His family have always denied the claims.
• That 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 that their implementation of this approach has been too slow.
• That the inquiry has done valuable work to date in a number of areas but must demonstrate this more clearly.
• That the inquiry needs rebalancing to ensure sufficient attention is paid to making recommendations for the future.
• That the inquiry’s commitment to exposing past failures of institutions to protect children from sexual abuse should remain unchanged.
• That the inquiry needs to publish a regular timetable of its activity starting with 2017/18.
• That the governance of the inquiry needs revising to provide stronger accountability and oversight of the programme of work.
• That those with an interest in the inquiry’s work should have more opportunity to engage with it.
• That the inquiry’s relationship with victims, survivors and others should be kept under constant review.