THE BBC's botched Newsnight programme failed to complete "basic journalistic checks", an official report concluded today.
And there was confusion about who had the ultimate responsibility for "final editorial sign-off" on the story which mistakenly implicated Lord McAlpine in a child sex abuse scandal.
A report by the BBC's Scotland director Ken MacQuarrie into the Newsnight blunders found the programme's editorial management structure had been "seriously weakened" as a result of the editor having to step aside over the Jimmy Savile scandal, and the departure of the deputy editor.
The mistakes led to the departure of director-general George Entwistle on Saturday night.
The problems in the programme stemmed from two different sign-off processes being put in place as a result of continuing inquiries into Savile.
Mr MacQuarrie's report said there was a "separation between 'business as usual' stories and 'Savile-related' stories", with a separate chain of command for anything to do with Savile.
He said: "It was not clear whether this story was regarded as Savile-related or not, or when that decision was made and communicated: a clear decision on this does not appear to have been taken until lunchtime on Friday 2 November.
"As a consequence there was ambiguity around who was taking the ultimate editorial responsibility for the Newsnight report, particularly in the days leading up to the day of transmission."
Mr MacQuarrie went on: "There was a different understanding by the key parties about where the responsibility lay for the final editorial sign-off for the story on the day."
And he said there were shortcomings in the quality of the journalism.
"During the editorial decision-making process, some of the basic journalistic checks were not completed," he said.
"Specifically, identification was not confirmed by photograph with the first victim. The second victim could not be traced in order to provide up-to-date corroboration."
Although legal advice was sought over the report, no right of reply was offered to the unnamed individual at the centre of the allegation.
The programme featured an interview with Steve Messham, an abuse victim who said a senior political figure of the time had abused him. He later said he had wrongly identified his abuser and apologised.
At the time of the broadcast, the programme's editor Peter Rippon had stepped aside as a result of the Savile furore. An independent inquiry, the Pollard Review, is looking into the circumstances behind the shelving of a Newsnight report late last year into the late DJ's abuse.
A blog written by Mr Rippon about the decision-making - and on which both Mr Entwistle and BBC Trust chairman Lord Patten had relied - was found to have contained inaccuracies.
The BBC's executive board called the failings "unacceptable". Earlier today it brought in a single chain of command for news output once again.
And it is now seeking "as a matter of urgency" to fill a vacancy for a non-executive director of the BBC with a senior external figure with a background in "overseeing journalism".
The BBC Trust said tonight that Mr MacQuarrie's findings of "serious failures" were "very concerning".
A spokeswoman said: "It is clear from the MacQuarrie report on the November 2 Newsnight that there were serious failures in the normal checks and balances that the Trust expects from BBC journalism, and these were compounded by the confusion created by the dual reporting structure in news established during the Pollard inquiry. This is very concerning.
"The measures that Tim Davie has put in place are sensible and appropriate while the inquiry carries out its work, and we note that consideration is being given to further action in respect of the November 2 Newsnight.
"We expect to receive regular updates on this issue from the acting director-general as he works with the utmost urgency to restore public confidence in the BBC and the integrity of its journalism."
The BBC said Peter Johnston, director of BBC Northern Ireland, had been involved in the decisions about the Newsnight report.
A spokesman said: "The sequencing of events around this report has been reviewed by Ken MacQuarrie and the BBC has now published a summary of findings and actions. The next stage of this process is now under way.
"It will, amongst other things, seek to clarify decision-making roles and responsibilities in relation to the Newsnight report. We expect that these investigations will be concluded as quickly as possible. In the meantime, we will not be making any further comment."