Allegations of bullying and sexual assault at the headquarters of the national child abuse inquiry have not been taken seriously enough, a Commons report has claimed.
In a fresh blow for the troubled inquiry, MPs also warned confidence in its ability to deliver on objectives in a "timely and effective way" has been "seriously diminished" after a catalogue of problems.
The Home Affairs Committee pointed out that experienced counsel have been departing from the probe at an "alarming rate".
Ben Emmerson QC, the most senior lawyer appointed to the Independent Inquiry into Child Sexual Abuse (IICSA), resigned at the end of September following an allegation that he sexually assaulted a female "inquiry worker" in the lift at its offices - a claim he has denied.
The MPs said the inquiry has reportedly denied receiving any complaint. The alleged victim gave an account of the incident on the day it happened, but did not want the incident to be investigated, according to the BBC.
Mr Emmerson also categorically denies bullying or any other misconduct.
The committee's report said: "It is not for us to pass any comment on the allegations made in the media about the former counsel to the inquiry, which he has categorically denied.
"We are not in a position, and it is certainly not our responsibility, to assess either the facts of the case or the details of the processes that the inquiry pursued.
"However, on the basis of the evidence we have seen, we do not believe that IICSA has taken seriously enough its responsibility to pursue allegations of bullying or disclosures of sexual assault within the inquiry.
"Nor do we believe it has done enough to demonstrate publicly that it has a robust approach to such matters."
As part of their review, MPs sought the views of former counsel on their experience of working with the inquiry.
But the report said that three out of four who had responded felt unable to provide substantive submissions on the basis that the inquiry had not waived its confidentiality and privilege rights.
In a letter, the solicitor to the inquiry said its chairman and panel "do not waive their rights to the confidentiality of the information the committee is currently seeking", adding that they take this position "because it is important that their work is not affected or impeded by outside influence".
MPs said the inquiry would benefit from "greater transparency about its approach and greater public clarity about the different kinds of work it is undertaking".
The probe has been plagued by problems since it was set up by then home secretary Theresa May in 2014.
Described as the most ambitious public inquiry ever launched in England and Wales, there are suggestions it could cost more than £100 million.
In the latest setback, last week one of the largest victims' groups involved withdrew from the probe, branding it an "unpalatable circus".
The development sparked calls for chairwoman Professor Alexis Jay to be replaced - but she has been backed by the Government.
Labour MP Yvette Cooper, chair of the committee, said: "This Inquiry is far too important to be sunk by problems. That's why urgent action is needed to sort them out. Survivors of abuse deserve nothing less."
Prof Jay - the fourth person to lead the inquiry - announced that it will invite an external senior legal figure to review some of the issues raised in the committee's report.
"While I am confident that our safeguarding and dignity at work procedures are robust, I recognise the impact of recent speculation and commentary about them," she said.
The former senior social worker said: "Nobody is more determined to deliver a successful inquiry on behalf of victims, survivors and the wider public than the panel and myself.
"We recognise that the past few months have been difficult for the inquiry and for the victims and survivors who have placed their trust in it.
"I am personally sorry for any unnecessary anxiety the inquiry may have caused to victims and survivors during this transitional period."
She will publish a review of how the inquiry operates in the coming weeks."While this will not alter our terms of reference, I believe it will make the work of the inquiry more transparent and set out a clear path for how the inquiry will progress," Prof Jay said.
Elsewhere the MPs criticised the inquiry's former chairwoman Dame Lowell Goddard, accusing her of refusing to provide oral evidence to the committee.
Earlier this month the New Zealand high court judge said she had never declined to provide oral evidence to the committee.
In a letter to the committee Dame Lowell said she had a duty to maintain judicial independence and had volunteered detailed written reports, adding that she was "not aware of any matter which remains unanswered".
Home Secretary Amber Rudd said the inquiry "has a vital role to play in exposing the failure of public bodies and other major organisations to prevent child sexual abuse".
She added: "I am confident of the inquiry's ability to confront the appalling reality of this abuse and my department is absolutely committed to supporting it in doing so. We owe it to victims and survivors to get this right."