Raymond Stevenson, who has spoken about being physically abused during his time at the Shirley Oaks home in the 1970s, said the group’s members had voted “overwhelmingly” on Saturday to pull out of the inquiry.
Mr Stevenson told the BBC that the group “felt relieved not to be part of this mangled attempt to get belated justice for our members” and he called the inquiry an “unpalatable circus”.
He added: “The inquiry has just lurched from disaster to disaster and we do not believe Alexis Jay, the chair, is the right person to wrench open the Pandora’s box of historical lies and cover-ups that have happened over the decades.”
The inquiry has been beset by difficulties since it was set up in July 2014 to investigate allegations made against local authorities, religious organisations, the armed forces and public and private institutions in England and Wales, as well as people in the public eye.
Three chairwomen – former president of the High Court Family Division Baroness Butler-Sloss, her replacement, leading lawyer Dame Fiona Woolf, and Justice Goddard, a New Zealand high court judge – have already stood down before Prof Jay took her place.
A number of senior lawyers on the inquiry have also quit – the most recent of which was Aileen McColgan, who resigned on Wednesday amid concerns about the inquiry’s leadership.
Shirley Oaks Survivors Group had threatened to withdraw before, questioning the inquiry’s independence and claiming that the Home Office, which sponsors the inquiry and provided some of its staff, had a role in covering up abuse in the past. Now it is planning to publish the results of its own investigation.
Ms Rudd has also come out in defence of Prof Jay and said: “We owe it to victims and survivors to get behind the inquiry, and its chair.”
She added that the inquiry had a “vital role to play in exposing the failure of public bodies and other major organisations to prevent child sexual abuse”.
But the group said she was planning nothing more than a “social work talk shop”, which it said would achieve nothing, and described her as “an uninspiring leader”.
Their local MP for Streatham, Mr Umunna, told BBC Radio 4’s Today programme he was also concerned whether Prof Jay would be able to “bring the heft and forensic capacity of a judge” to the inquiry.
He also said there was concern about her social work background because “for many of the survivors… a lot the perpetrators came from that profession”, and further concern about the “severe dysfunction” in the legal team.
“So for all those reasons I don’t have confidence in this chair and I think we need a new one,” he said.