Image copyright AP

The child sex abuse inquiry dropped an investigation of its most senior lawyer despite a disclosure of alleged sexual assault.

Ben Emmerson was suspended in September over concerns about his conduct, but the suspension was lifted the next day when he resigned, allowing him to keep working for the inquiry for two months.

The inquiry faces claims it failed to fully investigate potential wrongdoing.

Mr Emmerson categorically denies sexual assault, bullying or other misconduct.

The inquiry denies it received any complaint of sexual assault.

It said it had suspended the QC because it was "very concerned" by aspects of his leadership.

BBC Newsnight has learned the inquiry was also aware that an inquiry worker had alleged Mr Emmerson had sexually assaulted her in a lift at the inquiry's offices in Millbank in central London in early September

The woman had given an account of the incident on the same day, but did not want the incident to be investigated. Newsnight understands inquiry chairwoman Prof Alexis Jay and the panel had been informed of the disclosure.

The inquiry has insisted that no complaint was made but when asked specifically if it could confirm that neither the chair nor any members of the panel had been made aware of a disclosure of alleged sexual assault, irrespective of any complaint having been made, the Inquiry declined to make any further comment.

Image copyright PA Image caption Last week Prof Jay told MPs that Mr Emmerson was continuing to work for the inquiry from home

Mr Emmerson was suspended on 28 September.

Prof Jay said at the time: "The inquiry has recently become very concerned about aspects of Mr Emmerson's leadership of the counsel team. He has therefore been suspended from duty so that these can be properly investigated."

The following day Mr Emmerson resigned, saying in a letter: "It has become clear to me that I am not the person to take this review forward on your behalf. It is now time for someone else to take the helm with a different leadership of the counsel team." No reference was made to his suspension.

At the time, Prof Jay issued a tribute to the outgoing counsel: "He has made an enormous contribution to the inquiry and we wish him well."

She also echoed his explanation of the departure: "Mr Emmerson has stepped down at this time because he considers that after two years at the helm it is now time for someone else to take the role forward and provide leadership for the counsel team."

Last week Prof Jay told MPs that Mr Emmerson was continuing to work for the inquiry from home, writing a handover document for his successor, who is yet to be announced.

The BBC understands he is working for the inquiry for four days a week, for two months.

As lead counsel to the inquiry Mr Emmerson was being paid £1,700 a day. He is likely to be paid around £55,000 for days worked after his resignation.

Image copyright Matrix Chambers Image caption Mr Emmerson was suspended on the 28 September. He resigned the following day

Labour MP Lisa Nandy told Newsnight the failure to investigate the alleged sexual assault was "the latest and most serious to date in a series of allegations that have emerged into the public domain in recent weeks".

She said: "They paint a picture of an inquiry that was set up in order to shine a spotlight on institutions that had become characterised by denial, secrecy and cover-up taking on some of those very characteristics itself."

The allegation of sexual assault is unproven. A lawyer for Mr Emmerson said on Thursday night: "Mr Emmerson categorically denies any allegation of sexual assault, or bullying or other misconduct at the inquiry."

Critics say that whatever the truth or otherwise of the sexual assault allegation, the inquiry's handling of concerns about Mr Emmerson has undermined the inquiry's credibility.

Ms Nandy said: "These latest allegations raise serious questions of confidence for survivors. If this inquiry is to succeed then it must proceed on a completely different basis based on transparency and openness."