South Yorkshire police and crime commissioner Shaun Wright has resigned from the Labour Party, but insisted he would not leave his post.
Mr Wright's resignation came after Labour threatened to suspend him unless he stepped down in the wake of a damning report into child abuse in Rotherham.
He has faced repeated calls to quit because he was the Rotherham Council cabinet member for children's services between 2005 and 2010.
But in a statement he said: "I formally tender my resignation from the Labour Party. However, I remain committed to, and intend to remain in, my role as an Independent Police and Crime Commissioner for South Yorkshire."
Mr Wright defended a two-decade record in public service and insisted protecting vulnerable people was his number
one priority as commissioner, a post to which he was elected in 2012.
His statement, posted on the official website of the South Yorkshire police and crime commissioner, said: "I have had to make the difficult decision to stand down from the Labour Party and it's with deep regret that I've come to that decision.
"I've dedicated my career and life to serving the public of South Yorkshire. As a father, and a citizen of South Yorkshire, my thoughts are with the victims and their families and I reiterate my apology to them and take full responsibility for my part in the collective failures which took place at Rotherham Council during the time I was in office and indeed to that end I resigned in 2010.
"I stand by my earlier comments that I've taken that experience to deliver a major transformation in the way South Yorkshire Police deals with horrific crimes such as child sexual exploitation, and much progress has been made since I was elected as commissioner in terms of supporting victims, taking preventive action, increasing awareness of the issue and bringing criminals to justice.
"I was elected to deliver the people's policing and crime priorities in South Yorkshire and I intend to see that duty through by leading the force on that urgent, and fundamental, journey of improvement for the sake of past, present and potential victims, who are the most important people in all of this."
Shadow police minister Jack Dromey earlier confirmed Labour would have suspended Mr Wright from the party today had he failed to resign from his £85,000-a-year post.
Labour is powerless to stop Mr Wright from continuing as an independent for the rest of his term in office.
Mr Dromey told Newsnight last night: "(Mr Wright) should resign. He had the power to act and he did not use that power to defend the powerless.
"He needs therefore to accept responsibility. If he does not resign then he will be suspended tomorrow morning."
Mr Dromey said there needed to be an investigation by the Independent Police Complaints Commission to ensure South Yorkshire Police and its officers were properly held to account.
Mr Dromey's intervention came at the end of a day in which Home Secretary Theresa May appeared to back calls from Mr Wright's party that he had to quit.
She said: "Shaun Wright obviously has had involvement in this, both as his role as a councillor and obviously he's now the police and crime commissioner.
"It's not my job as Home Secretary to hire and fire police and crime commissioners. The whole point of them is that they are elected by the people, so ultimately it is a choice for the electorate.
"But I believe his own party have called for him to resign. I believe he has real questions to answer and I think in the circumstances he should heed those calls."
Mr Wright was the council cabinet member responsible for children's services in Rotherham from 2005 to 2010, in the middle of a 16-year period when, according to the report, 1,400 youngsters suffered widescale sexual exploitation
including gang rapes, grooming and trafficking.
So far he has resisted pressure for him to leave the post, insisting he had no knowledge of the "industrial scale" of child abuse when he was a Labour councillor in the town.
Mr Wright said he believed the report's author, Professor Alexis Jay, should have gone further in naming officials responsible for the failings identified in her report.
But Prof Jay has cast doubt on the assertion that Mr Wright did not know about what was happening in the town.
She said: "Part of my remit was to identify what information was available to key people in positions of influence throughout that time.
"And there was certainly a very great deal of information available from an early stage; indeed from at least 2001, both through a youth project which did outreach work with these young victims and children's social care.
"Names of potential perpetrators, car registration numbers, a very great deal of detail. Really by April 2005, it seemed to me that nobody could say 'I didn't know'."
Prof Jay's report revealed that although the majority of perpetrators were described as "Asian" by victims, councillors did not engage directly with the Pakistani-heritage community to discuss how to tackle the issue and some staff were nervous about identifying the abusers' ethnic origins "for fear of being thought racist".
Harry Harpham, chairman of South Yorkshire's police and crime panel, said he believed Mr Wright's position had become "untenable" and called on him to stand down.
The Labour councillor told BBC Radio 4's Today programme that he had been unable to speak to Mr Wright but insisted he would be seeking an urgent meeting to communicate his view.
He went on: "He should resign at the earliest opportunity.
"He can only be removed from office by resigning or unless he commits a criminal offence.
"We are not able to remove him, however, I will seek an urgent meeting with Shaun to let him know my position."
Asked whether he thought lessons had been learned, Mr Harpham said he would be meeting with the chief constable of South Yorkshire Police to discuss the findings of the report.