DIAMONDS may not be for ever. Gem merchants are concerned that a new Hollywood film starring Leonardo DiCaprio and exposing the violent underworld of “conflict diamonds” may dim their glittering reputation.

The Oscar-nominated actor has signed up to make The Blood Diamond, in which he will portray a smuggler embroiled in the civil war in Sierra Leone, where guerrillas systematically mutilate miners to enforce their grip on the west African nation’s export trade.

DiCaprio took the role after speaking to experts from Survival International, the London-based human rights organisation whose lobbying also influenced the rapper Kanye West to compose his recent hit single Diamonds from Sierra Leone.

De Beers, which has dominated the trade in diamonds since 1930, has expressed misgivings about the film, which will start shooting next spring.

At a mining conference in Cape Town, Jonathan Oppenheimer, head of the company’s South African operations, warned that the movie could undermine efforts to maintain the image of its diamonds as “untarnished and ethical”.

Oppenheimer said that a recent global trade agreement called the Kimberley Process, which seeks to authenticate the origins of the £500m of new stones sold each year, had curbed the number of conflict diamonds, but warned that the film could undo much of its positive effect.

“Can you imagine this film’s impact on the audience in America if the message is not carried through that this is something of the past,” said Oppenheimer, whose family commissioned the marketing slogan “diamonds are for ever” in 1947.

While De Beers insists that “conflict diamonds” account for fewer than 4% of the world’s new gems, lobbyists say that the true figure is closer to one in four. “Anything that shines a light on the atrocities carried out for such diamonds is to be welcomed,” Amnesty International, the human rights group, said last last week.

Hollywood and diamonds have been linked since Marilyn Monroe claimed in the 1953 film Gentlemen Prefer Blondes that they were a girl’s best friend. Elizabeth Taylor set the trend towards ever bigger stones when she married Richard Burton for the first time 11 years later.

Recent films have focused a colder eye on the business behind the symbol of love. The most recent James Bond movie, Die Another Day, revolved around diamonds from Sierra Leone.

This week sees the British premiere of Lord of War, starring Nicolas Cage as a Ukrainian arms dealer, which highlights government fears about links between illicit diamonds, arms and terrorism.

DiCaprio, dismissed by some in the past as a baby-faced party animal, said recently that he wanted to use his fame for a greater good. “In this town you can either be a vain movie star or you can try to shed some light on different aspects of the human condition,” he said.

Friends say that his attention was drawn to the African diamond trade by his girlfriend Gisele Bundchen, the Brazilian supermodel. Bundchen knows the British model Lily Cole and the Somali-born Iman, both of whom stopped modelling for De Beers after the company was accused of expelling Kalahari bushmen from a mining area. De Beers says that the 2,000 bushmen moved out of the Botswana region of their own accord.

Americans buy 55% of the world’s diamonds compared with 3% that go to Britain. Although it remains to be seen whether the new film will change opinion in America, there are already calls for a stricter enforcement of the Kimberley agreement and for buyers of diamonds to be more aware of their origins.

West annoyed fellow rappers recently when he accused them of being childishly obsessed with “the bling”, or show-off jewellery, a fashion that is fuelling the demand for ever-larger diamonds which are most easily obtained from African war zones.

“Black Americans in particular should be ashamed of the bling which comes seeped in black Africans’ blood,” the rapper said.

“They should ask more questions when they are buying their watches and chains. Like what is the true cost of the bling?”

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