L’Oréal, the French cosmetics giant, whose advertising campaigns proclaim “because you’re worth it”, was found guilty of racial discrimination for considering black, Arab and Asian women unworthy of selling its shampoo.

France’s highest court was told that the group had sought an all-white team of sales staff to promote Fructis Style, a haircare product made by Garnier, L’Oréal’s beauty division.

The word went out that Garnier’s hostesses should be BBR — “bleu, blanc, rouge” — the colours of the French flag. The expression is widely recognised in the French recruitment world as a code for white French people born to white French parents, a court was told, in effect excluding the four million or so members of ethnic minorities in France.

La Cour de Cassation, the equivalent of the US Supreme Court, said that the policy was illegal under French employment law, upholding a ruling given by the Paris Appeal Court in 2007.

The judgment was a significant blow to the image of the world’s biggest cosmetics group, which has spent millions of dollars in global advertising campaigns featuring stars such as Andie MacDowell, Eva Longoria, Penélope Cruz and Claudia Schiffer.

That image already suffered a battering when L’Oréal executives were forced to deny claims that they had lightened the singer Beyoncé Knowles’s skin for a campaign last year. The ruling also hinted at widespread prejudice among French shoppers since L’Oréal believed that they were more likely to buy shampoo from white sales staff, the court was told.

The ruling will fuel anger among black and Arab French people, who complain that they face widespread discrimination when seeking employment.

The court ruled that Adecco, the temporary recruitment agency whose Districom division hired the hostesses, was also guilty of racial discrimination. The Paris Appeal Court had fined both L’Oréal and Adecco €30,000 (£25,500) and ordered them to pay a further €30,000 each in damages to SOS Racisme, the anti-racist campaign group, which brought the case. The court upheld the fines but told the appeal court judges to reconsider the damages.

L’Oréal expressed “disappointment” at the judgment, which ends three years of legal wrangling over the discrimination claims. Adecco declined to comment.

Samuel Thomas, the vice-chairman of SOS Racisme, described the ruling as a “very great victory”. He said: “Whatever the size of the company, none is able to escape prosecution.”

The court was told that a Districom executive had sent a fax to its headquarters in 2000 saying that Garnier’s hostesses should be aged 18 to 22, wear size 38 to 42 clothes (British sizes 8 to 12) and be “BBR”.

Prosecutors said that Garnier wanted to exclude members of the ethnic minorities on the ground that they would be less likely to sell its shampoo in French shops. The court was told that only 4.65 per cent of the hostesses hired for Garnier’s campaign were black, Asian or Arab.

Before the BBR fax went out, the agency had been offering a pool of candidates in which 38.7 per cent were from ethnic minorities, suggesting that they had been blocked during the final stages of recruitment.

Districom employees said that they were given oral instructions to favour white sales staff. But Thérèse Coulange, the deputy managing director of Districom, who sent the fax, said that she had merely wanted hostesses able to “express themselves correctly in French”. She said that the fax had been a personal initiative and not the implementation of company policy.

Laurent Dubois, Garnier’s former managing director, told a lower court that he had “never given the slightest order to discriminate against anyone” and described racial prejudice as “foreign to L’Oréal’s genes”.

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