BBC's director general resigns

In a brief statement outside BBC headquarters in London, Entwistle said that he has decided to do the "honourable thing" and step down.

"When appointed to the role, with 23 years' experience as a producer and leader at the BBC, I was confident the trustees had chosen the best candidate for the post, and the right person to tackle the challenges and opportunities ahead," he said.

"However, the wholly exceptional events of the past few weeks have led me to conclude that the BBC should appoint a new leader."

"While there is understandable public concern over a number of issues well covered in the media... we must not lose sight of the fact that the BBC is full of people of the greatest talent and the highest integrity. That's what will continue to make it the finest broadcaster in the world," Entwistle concluded.

Standing alongside him, the chairman of the BBC Trust, Lord Patten said it was "one of the saddest evenings" of his public life".

"At the heart of the BBC is its role as a trusted global news organisation," he said.

"As the editor in chief of that news organisation George has very honourably offered us his resignation because of the unacceptable mistakes - the unacceptable shoddy journalism - which has caused us so much controversy."

"He has behaved as editor with huge honour and courage and would that the rest of the world always behaved the same," Lord Patten said.

Tim Davie, currently chief executive of BBC Worldwide, will take over as acting Director General from Sunday.

Earlier on Saturday, Entwistle had said the BBC should not have aired the programme and admitted it further damaged trust in a broadcaster already reeling from the fallout over its decision not to air similar allegations against one of its star hosts.

On Friday, BBC apologised for its 2 November "Newsnight" TV show on alleged sex abuse in Wales in the 1970s and 1980s.

During the program, victim Steve Messham claimed he had been abused by a senior Conservative Party figure.

The BBC didn't name the alleged abuser, but online rumours focused on Alistair McAlpine, a Conservative Party member of the House of Lords.

On Friday, he issued a fierce denial and threatened to sue.

Messham then said he had been mistaken about his abuser's identity and apologised to McAlpine, prompting fury over the BBC's decision to air the report and the suspension of investigative programmes at "Newsnight."

Before his resignation Enwistle insisted that he was not aware of the programme before it was broadcast - saying in hindsight he wished the matter had been referred to him.

But that stand drew incredulity from politicians and media watchers wondering how he could have allowed a second botched handling of a high-profile child sex-abuse story so soon after the broadcaster was pitched into crisis over allegations against its late TV host Jimmy Savile.