The BBC's George Entwistle has resigned as director general amid growing anger over the broadcasting of child abuse allegations that wrongly implicated a former senior British Conservative politician.
In a statement issued by the BBC, Mr Entwistle said that as DG he is also Editor-in-Chief and responsible for all the content broadcast.
He said that the wholly exceptional events of the past few weeks have led him to conclude that the BBC should appoint a new leader.
Mr Entwistle was appointed to the job just two months ago.
He faced widespread criticism since a rival broadcaster carried charges last month that former BBC presenter, the late Jimmy Savile, was one of Britain's most prolific sex offenders.
Condemnation grew after the corporation made an embarrassing apology yesterday following an admission that the BBC's flagship news programme aired a mistaken allegation that an ex-politician sexually abused children.
Speaking outside the BBC centre in London, he said he had taken the decision "in the light of the unacceptable journalistic standards of the Newsnight film broadcast on Friday 2nd November" because he was editor-in-chief.
Mr Entwistle earlier today admitted that the Newsnight report which led to Lord McAlpine of West Green being falsely identified as a paedophile should never have been shown.
British ministers and MPs are demanding an explanation as to why the latest crisis had erupted so soon after the Jimmy Savile child abuse scandal.
An urgent report he commissioned from BBC Scotland director Ken MacQuarrie into the Newsnight report is due on his desk tomorrow.
An "immediate pause" to all Newsnight investigations has been announced.
Mr Entwistle told the BBC Radio 4 Today programme: "We should not have put out a film that was so fundamentally wrong.
"What happened here is completely unacceptable. I have taken clear and decisive action to start to find out what happened and put things right."
Mr Entwistle admitted the corporation was facing a "bad crisis" of trust in the wake of the Savile scandal - including a decision to drop a Newsnight investigation exposing the late DJ as a serial child abuser.
Although the programme did not name Mr McAlpine, there have been indications that he now intends to sue the BBC after it led to him being identified on the internet.
Earlier, Mr Entwistle insisted that he had no intention of resigning, although he accepted that his future now lay in the hands of the BBC Trust.
"I am doing the right things to try and put this stuff straight. I am accountable to the Trust in that endeavour. If they do not feel I am doing the right things, then obviously I will be bound by their judgment," he said.
Mr Entwistle said that despite the storm over the dropping of Newsnight's Savile investigation, he had not been alerted that the programme was planning a report on the North Wales children's home scandal.
He said that he had also been unaware of a tweet 12 hours before the programme was broadcast, from the Bureau of Investigative Journalism - which worked on the report - suggesting it was going to identify a senior political figure.
"I didn't see that tweet. This tweet was not brought to my attention so I found out about this film after it had gone out," he said.
"In the light of what has happened here I wish this was referred to me, but it wasn't. I found out about the film the following day."
At one point he was challenged by Today presenter John Humphrys as to why he failed to take a more active interest in what was happening - even though he was the BBC's editor-in-chief.
"So there is no natural curiosity, you wait for somebody to come along to you and say 'Excuse me director general, but this is happening and you may be interested'?" Mr Humphrys demanded.
"You don't look for yourself, you don't do what everybody else in the country does, read newspapers, listen to everything that's going on and say 'What's happening here?"'
Mr Entwistle said that he only became involved if a programme was referred to him for his attention.
He said that Mr MacQuarrie needed to establish why things had gone so badly wrong on Newsnight, despite the appropriate referrals having been made.
"From the inquiries I have been able to make so far, this was a piece of journalism referred to senior figures within news, referred up to the level management board, and had appropriate attention from the lawyers," he said.
Among the issues that needed to be established was whether the abuse victim, Steve Messham, was actually shown a photograph of Mr McAlpine, and whether the peer was given a chance to respond to the allegations.
"Did the journalists carry out basic checks, did they show Mr Messham the picture, did they put allegations to the individual, did they think of putting allegations to the individual, if they did not, why not, and did they have any corroboration of any kind?" he said.
