Cannes, Sundance, Lake Como . . . El Fasher? In the past four years, the dusty airstrip in ravaged Darfur has seen a stream of celebrities dropping in to witness an unfolding crisis unseen by most of the world.

George Clooney and Angelina Jolie are just two who have lent their star wattage to lighting up the Darfur genocide in a way lesser-known activists could only dream of, helping to it elevate to one of the highest-profile causes in the United States.

Darfur is an almost unavoidable issue in America: cars sport Darfur bumper stickers, television advertisements show ordinary Americans reading horrific testimony from refugees, and on campuses students rally with a political fervour not seen since the anti-war movement of the Sixties.

“The celebrity engine has raised Darfur right up the agenda,” David Brown, of the anti-genocide group the Aegis Trust, explains. “It's helped bring awareness to a whole new audience who otherwise might not have paid attention. It's had an undeniable effect.”

Since 2003, at least 250,000 people have died and 2 million fled their homes in the Darfur region of Sudan, as mostly Arab militias have laid waste to the villages of black African tribespeople, backed with bombers and guns sent by Khartoum.

The conflict was little understood at the beginning, until Mia Farrow —already schooled in the art of activism — attended a lecture on the crisis in New York in 2004 and contacted the United Nations to volunteer as an ambassador.

Don Cheadle heard about Darfur while filming his role as the heroic hotel manager in the middle of the Rwandan genocide. “The similarities between Rwanda and Darfur revealed themselves pretty quickly. We were making a movie about a piece of history while another thing just like it was going on up in Sudan,” he said

Hotel Rwanda brought Cheadle a moderate measure of fame but with Farrow too easily dismissed by detractors as a radical, Darfur still lacked A-list advocates. Then came Ocean's Twelve, the Ocean's Eleven sequel, and with it some of Hollywood's most bankable stars with hours on set to hear Cheadle's entreaties over Darfur.

Clooney was quick to jump on board and in a serendipitous turn, the movie's other leading man, Pitt, hooked up with the famously conscienced Jolie, already involved through her UN work with the refugee fallout from Darfur. At the 2006 Cannes Festival the stars hijacked the premier of the third Ocean's film to highlight the crisis, replacing the party with a fundraisers for Cheadle's Not on Our Watch Foundation.

“All the guys have been to Sudan this year,” Jerry Weintraub, the film's producer, told reporters at Cannes. “They saw this huge genocide and nobody doing anything about it.”

Not everyone was immediately enthusiastic about welcoming Hollywood on board. As a grassroots movement, the Save Darfur Campaign got under way in 2003, when the Bush Administration used the term “genocide” officially to describe the crisis. That galvanised the Jewish community, spearheaded by Holocaust memorial groups, but also college students, who saw it as an issue on to which they could project their collective idealism, unlike the divisive issue of the war in Iraq.

The celebrities' success has been to bring the issue to an audience more comfortable with Heat magazine than The New Yorker. “You get it into the tabloids, on to daytime television, places that just wouldn't have covered it otherwise,” Aegis' David Brown notes. On Farrow's recent trip to London, he secured airtime for her on Loose Women and The One Show, programmes not usually associated with global affairs. Although most of Darfur's A-list advocates are notably liberal leaning, they have been successful in highlighting the humanitarian over the political. “It is not a political issue,” Clooney has said. “There is only right or wrong.”

Darfur activists have failed to convince many British celebrities of this. “We've approached a lot of them, but there is more suspicion,” Brown says. “Darfur is the nexus of the humanitarian and the political and in the UK if you don't know the political, you are more wary of getting involved.”

Darfur has also failed to set student campuses alight in Britain, unlike in the States, where many students still look back to the Sixties as a golden age of activism.

Some worry, however, that unless it succeeds in its goals, celebrity involvement may ultimatelytrivialise the issue. After all, for all their loud conscience-pricking, the celebrities have failed to halt the genocide. Clooney and Cheadle took celebrity activism to new heights when they travelled to Egypt and China to meet high-level officials to discuss its influence with Khartoum - an act of unilateral diplomacy. Last month Clooney was named a UN peace envoy, but his attempt to address the General Assembly on Darfur was scuppered by Russia and France, who objected to being lectured by a film star.

China listened, and bought into the fame-game when they hired Steven Spielberg as artistic adviser to the Beijing Olympics — a move it must now regret. Spielberg has been pressing Beijing to use its influence with Khartoum for more than a year, since the doughty Farrow challenged him as to whether he wanted to be known as the Leni Riefenstahl of the Games. Riefenstahl, the renowned German actress, dancer and filmmaker, put her talents into the service of Hitler's propaganda machine to film the Berlin Olympics of 1936.

It's a far cry from the traditional language and game of diplomacy played out in airless embassy rooms across the globe, but it may yet shape the ways that countries talk to each other on the international stage. Andrew Cooper, a Canadian professor has just written Celebrity Diplomacy, the first serious study of the phenomenon. Sometimes, he concludes, a celebrity may be just what is needed to bring an issue to the fore, from the bad-cop approach of Bob Geldolf to his more traditionally diplomatic friend Bono.

“Celebrities bring optimism and 'buzz' to issues that seem deep and gloomy,” he says. “Even if their lofty goals remain elusive, when celebrities speak, other actors in the global system listen.”

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