The troubled inquiry into historic child abuse has been hit by a fresh blow after an adviser was forced to resign.
Former child protection officer Peter McKelvie announced he had "reluctantly" concluded it would not be appropriate to continue in his role as a member of a panel set up to assist the probe.
He said: "I have today been advised that I am likely to be required as a witness in the inquiry's investigations, and that the inquiry may need to examine my work in pursuing allegations of CSA.
"In those circumstances it would not be right for me to continue to act in a consultative capacity, providing advice to the chair and the inquiry panel."
Mr McKelvie is seen as a key figure in the events leading up to the launch of the controversial police investigation into allegations of a VIP paedophile ring.
He claimed last year that at least 20 prominent paedophiles, including former MPs and including former MPs and government ministers, abused children for "decades" with even more establishment figures involved in covering up their activities.
In 2012, he took his concerns to Labour MP Tom Watson, who later raised the issue in the Commons.
Mr McKelvie was named as a member of the Victims and Survivors Consultative Panel (VSCP) after the inquiry finally started earlier this year following a string of delays.
Chairwoman Justice Lowell Goddard, a New Zealand judge, confirmed she had accepted Mr McKelvie's resignation.
She added: "I recognise and thank him for his contribution as part of the VSCP.
"I would also like to take this opportunity to stress that allegations concerning child sexual abuse related to Westminster are only one component of the Inquiry's work.
"As I said in my opening statement the Inquiry's terms of reference go far broader than this and encompass all institutions within England and Wales. This important work continues."
A statement from the panel said Mr McKelvie had offered his resignation "based on his likely inclusion as a witness in the investigative work of the inquiry".
It added: "We wish to express our gratitude to Peter for his enormous contribution to the work of our group and for his commitment over the last 30 years to protecting vulnerable children and victims."