The most senior lawyer working for the independent inquiry into historical child sexual abuse in England and Wales has been suspended from duty.
The inquiry said it had "recently become very concerned about aspects of Ben Emmerson QC's leadership" of his team and he had been suspended so these could be properly investigated.
The BBC understands more than one complaint has been made against him.
Mr Emmerson said he was "unable" to comment at this time.
The inquiry said press suggestions Mr Emmerson was considering resigning after raising disagreements over its future direction were untrue.
In a statement, it said: "They are not a matter on which he has advised the chair or panel."
The inquiry was set up in 2014 to examine whether public bodies including the police have failed in their duty to protect children from sexual abuse. It will also examine claims of abuse involving "well-known people".
Ian McFadyen, who was sexually abused at school, told BBC Radio 4's Today programme that the latest development was a "devastating blow" for survivors.
"Legal advice and quality of his expertise is essential, this [inquiry] has just been catastrophe after catastrophe," he said.
"I have met Mr Emmerson several times and he is somebody who I hold in high regard and who I think is trustworthy, so I'm more than upset."
Conservative MP James Berry, who was a barrister in the Leveson Inquiry into press practices, told Today that Mr Emmerson was a "very well experienced and intelligent lawyer".
But he added that he did not want to speculate on the reasons for his suspension.
Labour MP David Winnick, who sits on the Home Affairs Committee, said the inquiry was now in "crisis" and urged the home secretary to make a statement.
He also called for the recently-appointed chairwoman, Prof Alexis Jay, and Mr Emmerson to appear before the committee when it returned on 10 October.
The Times had reported that Mr Emmerson had wanted to reduce the inquiry's workload, but Prof Jay and Home Secretary Amber Rudd both said its scope would not be changed.
Mr Emmerson, who represented the widow of Alexander Litvinenko at the inquiry into the Russian dissident's death in London from radiation poisoning, is a deputy High Court judge, a visiting professor of human rights law at Oxford University and a leading international lawyer.
A spokeswoman for the home secretary said Mr Emmerson's suspension was a matter for the inquiry.
She added: "Our commitment to this inquiry is undiminished. We owe it to victims and survivors to confront the appalling reality of how children were let down by the very people who were charged to protect them and to learn from the mistakes of the past."
She confirmed the inquiry's terms of reference, which are set by the home secretary in consultation with the inquiry chairwoman, would not be changed.
The inquiry has been beset by a series of problems since it was originally announced by then Home Secretary Theresa May.
Prof Jay is the fourth person appointed to lead the investigation.
She was appointed after its third chairwoman, New Zealand judge Justice Lowell Goddard, resigned in August this year, citing the "magnitude" of the inquiry and the "legacy of failure" from its beginnings.
An attempt to start the inquiry in 2014 was abandoned after two proposed chairwomen resigned.
Baroness Butler-Sloss, stood down after just a week in July 2014, saying she was "not the right person" for the job. MPs and victims had raised concerns about her appointment because her brother, Sir Michael Havers, was attorney general at the time of some of the allegations being investigated.
Her replacement Dame Fiona Woolf resigned following questions over her links to establishment figures.