The troubled inquiry into historical child abuse has been hit by a fresh blow after an adviser was forced to resign.
Former child protection manager 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 as he is likely to be called as a witness.
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 (child sexual abuse).
"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's information is said to have led to concerns being raised by Labour MP Tom Watson over whether a minister had links to a past paedophile ring.
Police later found no evidence for such a claim, according to reports.
A string of controversial police inquiries were launched after Mr Watson's made a dramatic statement concerning historical abuse in the House of Commons in 2012.
Mr McKelvie has said he did not claim to the MP that there had been a "Westminster paedophile ring", according to the BBC.
He was a child protection manager in Hereford and Worcester and worked on the conviction of paedophile Peter Righton - a former consultant to the National Children's Bureau.
Righton, who is now dead, was also a founding member of the Paedophile Information Exchange (PIE), before he was convicted of importing child pornography.
Mr McKelvie was named as a member of the inquiry's victims and survivors consultative panel (VSCP)
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."
His departure is the latest in a catalogue of problems for the inquiry. Two previous chairwomen resigned before it was finally opened by Justice Goddard in July.
On Thursday it emerged that information provided by victims to the inquiry's website was accidentally deleted.
It is set to be Britain's largest ever public inquiry and is expected to take up to five years.