The veteran political broadcaster Jonathan Dimbleby has attacked the commercial enemies of the BBC for setting out to destroy it, and has urged audiences to rise up to defend the corporation.

“Even people within the BBC [who are] now beginning to stand up for it, fail to identify those vested interests. The Murdoch press is an enemy of the BBC for commercial reasons,” said Dimbleby, 70, in reaction to the release of the government’s green paper on the future size and remit of the corporation.

Making an unexpected intervention at a recording of Radio 4’s long-running current affairs comment show, Any Questions?, Dimbleby, brother of David and son of the BBC’s first war reporter, the late Richard Dimbleby, said the corporation’s opponents “have to be taken on by the BBC and by those viewers and listeners who own the BBC”. He added: “Go around the world, listen to what people say about the BBC, they think it’s astonishing we are having to think about whether or not it should survive.”

Dimbleby’s comments were not broadcast and are not included in the iPlayer version of the programme. His impassioned outburst was made over his radio microphone at the end of the recording in Leamington Spa, in response to a question from panellist and shadow business secretary Chuka Umunna and it came as the BBC Trust, the body that oversees the corporation, prepares to step up its information campaign.

The Observer has learned that the trust, which is expected to be disbanded or re-purposed next year, plans to go out fighting. This week it will announce a series of national events and audience surveys in an attempt to present government with evidence of the strength of public feeling.

A trust official said trustees were about to launch “the biggest ever version” of the research and public consultation work they regularly carry out. “There will be more intensive work than we have ever done in a single period and larger-scale research likely to reach more than 100,000 people,” he said. The trust was determined to broaden the debate and prevent a focus on perceived failings of the corporation.

A source close to the top of the BBC also claimed that, far from being cowed by criticism of its orchestration of support for the BBC in a letter signed by celebrities such as Michael Palin, David Attenborough and Emma Thompson, the BBC executive, led by director general Lord Hall, was to make the tone of the debate more combative, not less.

Dimbleby’s sentiments were echoed this weekend by Frank Cottrell Boyce, the writer behind the most popular recent display of British cultural values, the opening ceremony of the 2012 Olympics in London. “The UK enjoys a level of influence and soft power well beyond its economic or military weight. This is due almost entirely to the BBC,” Boyce told the Observer. “It speaks for the nation, in a way that HBO or Warner Brothers could never dream of speaking for America. And when the BBC speaks, what does it say? It says Doctor Who, Top Gear, In Our Time, Today, Strictly, Poldark, Cash in the Attic, Horizon, David Attenborough, Graham Norton … which translates as: here is a nation that is at ease with itself – innovative, creative, fun, serious, able to question itself and celebrate itself, diverse, eccentric and beautiful.”

Cottrell Boyce also argued that the “range of tones and ideas” embodied by the BBC formed a sense of national identity and provided the varied voice that politicians often claim Britain needs to defeat extreme ideologies and terrorism.

“We are always hearing we need a ‘counter-narrative’ to the threats that surround us,” he writes. “Where would that narrative come from, how would it be projected, if not by us as a nation, through our mouthpiece, the BBC?”

Piv Bernth, the producer of hit Danish thriller The Killing who now runs drama at the Danish Broadcasting Corporation, this weekend backed Dimbleby’s suggestion that the BBC was worth battling over: “Absolutely!. As a public service colleague from Denmark, I’m sure this kind of TV and radio is vital to a modern democracy. There must be one place in the media where the influence of private interests and stockholders is as little as possible.”

The decision to run The Killing on BBC4 was important, she added, not only for Danish drama but for international relations. “It took a lot of courage to broadcast a series with subtitles but that’s what a public broadcaster can do, be courageous and take chances. BBC4 started a new wave and now it’s less extraordinary. It widens our understanding of other people and their ways of living.”

The green paper brought before the Commons for discussion on Thursday by culture secretary John Whittingdale heralds three months of debate about the purpose of the BBC, what services and content it should offer and how it should be funded, governed and regulated.

“With so much more choice, we must at least question whether the BBC should try to be all things to all people,” Whittingdale told the Commons.

On Tuesday the Lords communications committee will question Radio 6 Music presenter Cerys Matthews, the Welsh songwriter who became famous as the lead singer of Catatonia, alongside Sir Peter Bazalgette, chairman of Arts Council England and former producer of Big Brother for Channel 4.

The committee is due to ask for their views on the role of the BBC in arts and culture; in education and training; and on the effect of financial cuts. The committee will also question Dr Roberto Suárez Candel from the European Broadcasting Union on the BBC’s standing overseas.