Lord Patten said he still believes the BBC, though not perfect, is "the greatest broadcaster in the world" in the wake of the Newsnight investigation which incorrectly implicated a senior former Tory in a child abuse scandal.
In a letter to BBC staff announcing the resignation of George Entwistle as Director-General, he said it was the corporation's top priority to address how last week's Newsnight investigation "went so horribly wrong."
He also urged for the corporation to continue to focus on how "the BBC's historic culture allowed Jimmy Savile to get away with his vile criminal activity for so long."
Here is the full text of the letter sent to BBC staff on Sunday :
Dear all,
It was with great regret that last night I accepted the resignation of George Entwistle as Director-General.
One of the reasons we appointed George was because he is an honourable man and his decision to stand down in the best interests of the BBC bears that out.
When I took the job of Chairman of the BBC Trust, I said that, while not perfect, at its best the BBC is the greatest broadcaster in the world.
I believe that today, just as I did then. The BBC is full of hugely talented and dedicated people making great programmes and finding innovative ways to bring them to audiences.
The vast majority of BBC staff have nothing whatsoever to do with this sorry episode and I regret that they are having to share in the pain.
The priority now is to address the very serious questions that still remain around the original decision not to pursue the initial Newsnight investigation, how last week's story went so horribly wrong and, most importantly, how the BBC's historic culture and behaviour allowed Jimmy Savile to get away with his vile criminal activity for so long.
We will decide what immediate action needs to be taken once Ken MacQuarrie's investigation into last week's Newsnight is complete. We will then look at what else needs to happen once the two independent inquiries have reported.
In the meantime, the Trustees have asked Tim Davie to stand in as Acting Director-General. I am sure that Tim will perform this role with authority and integrity, while we carry out the process of appointing a permanent successor as soon as possible.
Yours,
Lord Patten
Chairman, BBC Trust
Earlier Lord Patten made clear that he would resist calls for him to resign insisting his job was to ensure the BBC learned the lessons from what happened and from the inquiries under way into the Jimmy Savile child abuse scandal.
"I think that I now have to make sure that, in the interests of the licence fee payer and the audience, that the BBC has a grip, that we get ourselves back onto the road," he told BBC1's The Andrew Marr Show.
Lord Patten disclosed that unlike Mr Entwistle - who said that he had not known in advance about the Newsnight programme - that he had been aware of what was going on.
He said that he had been informed of a tweet from the Bureau of Investigative Journalism, which worked on the report, suggesting it was about to expose a senior political figure as a child abuser.
"I did subsequently ask whether the programme was being properly edited, whether it was being properly managed, and I was assured that it was," he said.
He said that the BBC now needed "a thorough, radical structural overhaul".
Ed Miliband echoed his words, tweeting late on Sunday: