Politicians should stop pressurising the BBC and the public should have more of a say in its future, the chairwoman of the BBC Trust says.

Writing in the Independent, Rona Fairhead said the BBC's future must be "driven by evidence and fact, not by prejudice and not by vested interest".

She also complains of MPs attempting to interfere in the broadcaster's affairs.

Culture Secretary John Whittingdale has said a debate is needed over whether the BBC should become more "precise".

The corporation's Royal Charter is up for renewal next year.

Ms Fairhead, who became the head of the BBC's governing body last October, said there is "good evidence" that audiences "very much" wanted the corporation to continue to be "part of their lives".

She added that people "believe that a significant public benefit arises from the existence of a strong, independent BBC that provides a universal service".

'Independent BBC'

Ms Fairhead said the public wanted independent scrutiny and regulation of the BBC, but that they wanted this done by a separate body representing licence fee payers, not by politicians.

"That independence has needed defending over decades, not just from governments but also from parliament, with a growing tendency in recent years for select committees to question BBC executives about detailed editorial decisions," she said.

"We believe that this charter review gives us a chance to codify the relationship between the BBC and the state, and the BBC and its public, so that the terms of engagement are clear, the processes transparent, and the BBC can be seen to be both accountable and independent."

She also said that the corporation "cannot sit still" when it came to creating and offering new technology.

"It has a strong history of initiating highly valued technological change - the iPlayer being only the most recent example.

"But the iPlayer is now more than seven years old - which makes it venerable in digital time-scales.

"Everyone wonders where the next great innovation in delivery will come from, so the BBC must have the technical and research capacity, if not to invent new technologies, at least to adapt and exploit them."

She goes on to say that the broadcaster is dealing with "ever-tighter funding constraints" along with "arguably the greatest external challenges in its lifetime".

While accepting that "the status quo is not an option", she says changes "should happen through a proper debate where the public's voice is heard loud and clear".

She added: "The BBC's future is simply too important to be settled behind closed doors."

'Editorial failures'

Mr Whittingdale has launched a Green Paper on the corporation's future, saying he wanted the corporation to "thrive".

But the corporation has said the review suggested "a much diminished, less popular, BBC".

It has already agreed to take on the cost of free TV licences for the over-75s, in return for some concessions, including linking the licence fee to inflation.

The Green Paper also said responsibility for regulation of the broadcaster could be transferred away from the BBC Trust, after incidents where the corporation had "fallen well short of the standards we expect".

Mr Whittingdale has cited "editorial failures" in the light of the Jimmy Savile revelations and the level of severance payments as sources of "disquiet".

The BBC has previously responded by saying public consultation should be a key part of charter review.