From Butch Cassidy and the Sundance Kid to All Is Lost, Redford has played men struggling to survive against long odds. From All The President's Men to Lions For Lambs, he has needled the establishment. As an environmental activist, long before it was fashionable, he has been hounded and pilloried and burned in effigy. It hasn't always been fun, but he relishes the challenge.

In his new film, Truth, Redford plays veteran television anchorman Dan Rather, who reported from Dallas on the day JFK was shot and became the face of CBS nightly news. Cate Blanchett plays his producer, Mary Mapes, who established her own journalistic reputation by breaking the story of American soldiers abusing detainees at Abu Ghraib prison in Iraq.

The movie is about the unwavering bond of loyalty and trust between Mapes and Rather, and how that relationship is tested as the accuracy and neutrality of their reporting comes under attack. It is based on Mapes' memoir, so Blanchett is the heart of the film, but Redford's restrained performance as a father figure trying to protect his surrogate daughter is a pleasure to watch.

"I have an unapologetic, uncontrollable crush on the man," Blanchett told talk-show host Jimmy Kimmel. "Because Bob has been so extraordinary in American culture generally, you forget what an extraordinary actor he is."

In a 60 Minutes report, Rather and Mapes alleged that President George W. Bush dodged the draft for Vietnam by enlisting in the Texas Air National Guard, and received preferential treatment once he got there. The piece aired two months before the US presidential election in 2004 and was immediately attacked by conservative news outlets claiming that the documents it relied on were forgeries.

Under pressure, CBS forced Rather to issue an apology and step down. Mapes was fired. Truth makes the claim that they were unfairly treated – victims of a right wing smear campaign and a spineless corporate media. It will open old wounds.

"I expect it's going to be controversial," Redford says, with a twinkle. "The other side's not going to sit there quietly. And I'm prepared to defend what the film has to say."

Redford first met Rather in 1976, when he enlisted the journalist's help to prevent the construction of a coal-fired power plant on the Kaiparowits​ Plateau, in his home state of Utah.

"It was an ugly time, because the plant did not get built, and all the people in those areas who thought they were going to get food put on their table blamed me," Redford says. "They used to say 'what does he know, he's an actor?' But then Reagan got elected and they had to find another argument."

Redford's standing in Utah has since recovered. "What changed it – it took about 30 years to do it – is the festival. It brings a lot of money in," he says.

The Sundance Institute, founded as a small-scale meeting of outsider film-makers at his ranch in 1981, now attracts 35,000 visitors and generates around $80 million each year, and has become a globally recognised brand promoting independent films.

At the press day for Truth in New York, I catch myself unconsciously checking out Redford's form. His blue cotton shirt is undone one button too far, it seems to me, and he's a bit on the lumpy side. But no sooner have I thought this, then I remember: he's 79 years old. Even matinee idols age.

He still has thick russet red hair, still plays tennis, still rides across the wilderness for hours and still drives his Porsche too fast. On the set of All Is Lost, as a sailor alone in a boat holed at the waterline, doing battle with the ocean, he did his own stunts and was proud of the beating he took.

In All The President's Men, filmed 40 years ago, Redford played Bob Woodward, an ambitious young journalist at The Washington Post who, together with his partner Carl Bernstein, set out to prove that the Watergate break-in was organised at the White House.

That film ends with a series of headlines tapped out on a typewriter, announcing that senior political figures have been sent to jail, culminating in the news that President Richard Nixon has resigned. There's no such happy ending in Truth. Mapes does get a measure of vindication, in the magnificent retort that Blanchett delivers to the company men judging her, but when the credits roll, she's discredited and out of work, and Rather is off the air.

"All The President's Men is about two people at the bottom of the ladder trying to get at the truth of something that was controlled by the powers that be. But they had the support of The Washington Post," Redford says. "Mary Mapes and Dan Rather were also uncovering something really serious, but they did not get the support from their bosses. So these guys got taken down, Woodward and Bernstein became heroes."

There is, to employ the film's somewhat ill-advised name, some truth in that. But it's also striking how far the popular image of journalism has fallen. In a Pew poll released last year in the US, just 28 per cent of respondents said journalists contribute a lot to society's well-being. Only lawyers and business executives were more disliked.

In historical dramas, such as Good Night, and Good Luck, journalists take risks to expose wrongdoing and speak truth to power. In contemporary films, like Shattered Glass, they trample on ethics to fabricate a good story. As a cable news producer in Nightcrawler, Rene Russo tells Jake Gyllenhaal's aspiring videographer: "Think of our newscast as a screaming woman, running down the street with her throat cut."

Truth attempts to buck that trend. Its reporters are honest and diligent, and punished out of all proportion for their mistakes.

"Who is going to know what the truth is when you have so many voices fighting on either side. Boy, it gets hard," Redford says. "What choice do we have except journalism? It's the only vehicle we can rely on, to get at the truth, but it's not easy."

Truth is out now.

Needling the powers that be

Throughout his career, Robert Redford has courted controversy in his choices of starring role, as well as his political activism. Here we round up some of his most provocative films.

The Candidate (1972) In this cold-blooded satire, Redford plays Bill McKay, an idealistic young politician who is forced to make a series of uncomfortable compromises on the campaign trail.

All The President's Men (1976) Redford met journalists Bob Woodward and Carl Bernstein soon after they broke the story of the Watergate break-in, and encouraged them to write a book. The film established his reputation as a "Hollywood liberal" and conservative hate figure.

Havana (1990) Redford caught more flak for this romantic drama, set on the eve of the Cuban Revolution and rather too sympathetic to Fidel Castro for right-wing tastes. Redford is said to have gone scuba-diving with Castro while researching the role.

Lions For Lambs (2007) In this searching examination of whether there can ever be a 'just' war, Redford plays a university professor who encourages his students to enlist in the US Army to fight in Afghanistan, with tragic results. Meryl Streep and Tom Cruise co-star.

The Company You Keep (2012) Can radicals ever escape their violent past? Redford's former member of the militant Weather Underground group finds his new life and identity under threat when a young journalist starts digging.