BBC Trust chair Rona Fairhead to stand down
BBC Trust chairwoman Rona Fairhead has announced she will step down early from her role and will not apply to head the corporation's new governing body.
A unitary board will replace the BBC Trust, the corporation's arms-length regulator, and its executive board.
Ms Fairhead said the prime minister had "strongly encouraged" her to take part in the new appointment process.
But, she added, it would be "better to have a clean break and for the government to appoint someone new".
The previous government, under David Cameron, had originally asked Ms Fairhead to continue until 2018 - moving from chairwoman of the Trust to lead the new unitary board.
But BBC assistant political editor Norman Smith said government sources described Prime Minister Theresa May as being not "overly impressed" by Mr Cameron's decision to appoint Ms Fairhead to the unitary board.
It is understood that Mrs May was concerned about the lack of transparency in the appointment process and felt the new post required different skills.
The decision to open the job up to other candidates was due to be announced on Thursday as part of a package of reforms of the BBC Trust.
Ms Fairhead's announcement, ahead of time, of her decision to go will be seen as an indication of strained relations between her and the prime minister.
Norman Smith, BBC assistant political editor
Most new prime ministers choose to distance themselves from their predecessors in order to signal change.
Rarely, though, has a new prime minister gone about dismantling and unpicking key decisions of their predecessor so quickly and so brutally as Theresa May.
The move to block the automatic appointment of Rona Fairhead as chair of the new BBC Board is just the latest example of Mrs May's readiness to rip up Mr Cameron's plans.
It follows from the very deliberate decision to give the go-ahead to grammar schools - a move Mr Cameron had strenuously resisted and made central to his modernising agenda.
Similarly, Mrs May has ordered a re-think over the Hinkley power station, tackling the deficit and the so-called "northern powerhouse".
What gives even more edge to Mrs May's actions is the fact that disowning chunks of David Cameron's legacy looks personal as well as political.
Hence her decision to cull Mr Cameron's friends and allies from the cabinet.
Ms Fairhead, the first woman to lead the BBC Trust, began her four-year tenure in October 2014.
It coincided with a renewal of the BBC Charter. In May this year a government White Paper unveiled major changes to how the BBC is run.
Following this, the government, under David Cameron, asked Ms Fairhead to continue until 2018 - and chair the new unitary board.
But it has since been decided to introduce an appointment process, a spokeswoman for the Trust said.
Ms Fairhead will step down when the new board begins its work early next year.
In a statement, Ms Fairhead said: "I took on leadership of the Trust to help stabilise, strengthen and develop the BBC following a very difficult period in its history and through Charter review. I was always clear that I was willing to serve for four years, after which I would continue my career in the private sector.
"I am proud of what I and my colleagues, both at the Trust and the BBC, have accomplished during the past two years. I believe the draft charter will secure the strong, confident and independent BBC that the public want and deserve."
Ms Fairhead said she intended to continue her career in the private sector "as I had always planned to do after my existing term ended in 2018".
BBC director general Tony Hall said: "Rona has made a real contribution to BBC and at a really important time for us. On behalf of all the staff, I'd like to thank her for that and wish her the very best for the future.
"We will continue to work together in the interests of licence fee payers until the new governance arrangements are in place."
A spokesman for the Department for Culture, Media and Sport said: "The government thanks Rona Fairhead for her service to the BBC. Full details of the BBC Charter will be announced shortly."
Ms Fairhead is a former Financial Times chief executive and has served on the boards of a number of multinational companies including HSBC and PepsiCo and held leadership positions with plane and train-maker Bombardier and with ICI.