BBC director general George Entwistle has fallen on his sword over the "unacceptable" Newsnight broadcast which wrongly implicated a senior former Conservative in a child abuse scandal.

In a brief statement outside Broadcasting House, Mr Entwistle said that he had decided to do the "honourable thing" and step down from his post.

"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."

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