In the eyes of many, Aichana mint Ebeid Beilil does not exist. As a member of Mauritania’s slave caste, she is almost invisible and the ruling classes are selectively blind to the fact that she once belonged to a light-skinned man.

This weekend, however, the West African state will confront one of its greatest taboos, when more than one million people go to 2,300 polling stations scattered through the Sahara to choose their first democratically elected president.

Forcing the unspoken issue into the open is Messaoud Ould Boulkheir, a former slave who watched his mother being beaten regularly by her Nomad masters. He is the only black Haratine representative among 19 mainly “White Moor” candidates.

Boulkheir, who was jailed three times by Mauritania’s military rulers, is the first member of the caste to run for office.

“The Haratine have long been left out of politics,” the 64-year-old campaigner told The Times. “I have decided to stand to show them the doors are not closed, and to end this culture of subservience. Some of them will follow me. Some will take time to follow me, and some will find it difficult because they have been brain-washed by their masters.”

At a recent rally, some people laughed when he spoke of equality: “It is difficult when you encounter this attitude, but that is the reality.”

Mauritania is a largely forgotten nation that sits on the shifting sands of black African and Arab culture and spans more than one million square miles of desert and dust. It has one of the highest rates of slavery in the world. “Paradise is under your master’s foot”, goes the local saying — only they can grant you freedom. Although slavery was formally abolished in 1981, hundreds of thousands of its three million-strong population remain in bonded labour.

The majority are Haratines, whose ancestry lies towards the southern border with Senegal and who have been subjugated and “arabized” by the northern Bidan — White Moors — who gave the country its name. Together, the groups make up two thirds of the population.

However, the enthusiastic support for Boulkheir and his antidiscrimination programme has encouraged hopes of a watershed in Mauritania’s poor human rights record.

International observers are satisfied so far with the elections, after a bloodless coup two years ago marked the end of two decades of brutal military dictatorship. About 1.4 million ballot papers have been printed and distributed by a Sussex-based company.

Boubacar Messaoud, the founder of the antislavery organisation SOS Esclaves, is lobbying each candidate to put in place new laws to eradicate a custom that has perpetuated class divisions for 800 years.

“People think of slaves in chains,” he said, crossing his wrists. “But these people are chained in their minds. Why does slavery still exist? Because we have no law punishing the masters. In some cases, the authorities will even help the master get an escaped slave back.”

Aichana, a quiet but assertive woman who believes she is 38, says slavery remains largely hidden. “Mauritania is full of slaves, but they are afraid to talk about the issue,” she said.

She, like her mother, was the slave of Mohammed Ul Mousa, the head of a White Moor family in Magta Lahjar, 125 miles (200km) east of Nouak-chott. Domestic drudgery was punctuated by beatings. “He treated us like animals. He would beat us with his hand, or whatever he could find. He hated us,” she said.

When he died Aichana and her family were divided among his relatives. She was delivered to his brother. Aichana fled, but when her master tracked her down it was another Haratine who suggested that she give him her two infant sons as compensation. Aichana did so, to be reunited three years later, with the help of SOS Esclaves.

She is now part of the emerging underclass of former slaves struggling to survive in the shanty towns outside the capital. Others who do manage to exchange unpaid domestic duties for work in the larger towns may never escape their slave status, with masters stepping in to claim their earnings.

Traditions are stronger in places such as Kiffa, an impoverished town 190 miles from the capital, where election tents promise equality and education from crackling loudspeakers.

For Abdullah Mustafa, a White Moor community elder, the dark-skinned boy serving mint tea to him and his family is a legitimate member of the household.

“I consider him one of the family. In our culture, when someone is working for you, you take him as your son. He can sleep anywhere in the house. If he decides to leave, I will give him his money. But he is comfortable here, he prefers to stay here. Ask him, and he will say this is true.”

Sidi ould Elemine says nothing and pours tea.

Mauritania

A largely desert country, Mauritania shares borders with Mali, Senegal, Algeria and the Sahara

It is one of Africa’s newest oil producers, with foreign companies poised to expand exploitation in the Chinguetti oil fields 50 miles offshore

The former French colony gained independence in 1960. After years of military regimes, a bloodless coup d’état in 2005 ended President Taya’s two decades of dictatorship

Among the candidates for election is Ahmed Ould Daddah, a White Moor and brother of Mauritania’s first president, Mokhtar Ould Daddah, who was ousted in a military coup 1978

The country is one of the few Arab countries to forge diplomatic ties with Israel — a provocative issue in the upcoming elections

Times Recommends

• How the fall of the Wall freed Nelson Mandela
• Iguacu, the world’s most spectacular waterfall
• How Harrods helped Burmese cats return