You can still see blood on the rocks that shaped the sly hiding place where they butchered Sello Chokoe. To the golden horizon in every direction the land is perfectly flat save for the husky remnants of a harvested maize crop and these rocks that form strange S-shaped parallel lines.

It was in this lonely place that the 10-year-old’s killers held him down while they chopped off his right hand, right ear and genitals before hacking a hole in his skull to take slivers of his brain. Then they ran away, leaving him to stumble 50 metres before collapsing. In keeping with the gruesome way in which such attacks are carried out, Sello was conscious during the whole unimaginable episode.

In the tiny village of Moletjie in Limpopo province, 250km (150 miles) north east of Johannesburg, Sello’s family are struggling to come to terms with what happened to the boy they say was always laughing. The loss of any family member is great, but the manner in which Sello was killed has traumatised his whole community. Because Sello Chokoe was harvested as surely as the maize in which he was found.

This is the world of muti murder, in which victims are chosen for their body parts to be taken for use in black-magic medicine. In South Africa alone, as many as 300 people a year are killed in this way to provide power, luck, health or money for “clients” with enough resources, and enough faith in ancient African beliefs, to put in an order for a fresh human harvest.

A belief in muti, Zulu for medicine, is deep-rooted in the sub-Saharan African psyche, from Nigeria to Benin, South Africa to Tanzania.

It usually relates to the traditional use of animals, herbs or plants in natural remedies. But there is a small, dark corner in the world of muti that advocates the use of human body parts, a corner that is not unique to Africa. There is growing evidence that its malevolent shadow has already spread to the UK.

The discovery of a boy’s headless torso floating in the Thames in 2001 provided the first clues that muti killing and had arrived on our shores. And now African and British experts believe that it is only a question of time before we will be visited by more muti murders of our own.

Sello was unlucky — any boy from his village could have been chosen. But he was the one who wandered past the muti harvesters as he was looking for a neighbour’s donkeys on July 30 at about 5.30pm.

“There must have been more than one attacker because it would take at least two people to remove a hand, an ear and genitals from a person who was fully conscious,” says Inspector Mohlaka Mashiane, of Limpopo police. The inspector is one of South Africa’s new breed of young professional police officers struggling to work against a backdrop of ignorance and a lack of resources.

“Another boy out collecting wood with his mother found Sello 50m from where the attack took place. He was groaning and trying to stand up. The boy ran back to the village to alert Sello’s mother, and the police and an ambulance were called. Medics did what they could until a helicopter arrived, but he slipped into a coma. He died after ten days.

“I saw the boy. It was terrible. His hand was gone, his ear and his genitals had been taken. And there was an awful gaping hole in the back of his head where you could see his brains. Everybody was terribly upset. I just kept wondering about his attackers, asking myself: ‘Where were their eyes while this boy’s blood was flowing? Where were their ears while he was screaming?’ ” There is nothing new in muti murder. According to Dr Gérard Labuschagne, the head of the South African Police Service’s investigative psychology unit, it has been practised for thousands of years.

Dr Labuschagne, who has the rank of senior superintendent in the force, advised Scotland Yard on the torso-in-the-Thames murder. His office in Pretoria is littered with pictures of muti killings. Here, a couple stand over their own son, butchered by them for luck. His head, arms, legs and torso arranged in neat piles. There, a muti man with three heads hidden in clay pots; the remnants of one body expertly butchered and dried out, hidden under a rug.

“A traditional healer usually advocates muti murder after having been consulted by a client,” says Dr Labuschagne. “A third party carries out the actual murder. The traditional healer, as a rule, is never involved in the murder. The reason for using human body parts is that they are considered to be more powerful than the usual ingredients or methods used because they contain the victim’s ‘life essence’.

“These usual ingredients may include roots, herbs, other plant material, animal parts and seawater. Characteristically, the traditional healer would consult the ancestors to determine the cause of the problem, and then would prescribe the treatment.

“Traditionally, the victim must be alive when the body parts are removed as this increases the ‘power’ of the muti.”

From his own experience of more than 30 muti murders and from consulting traditional healers, the overwhelming majority of whom abhor the use of human parts, Dr Labuschagne has established a dark pharmacopoeia of items that can be dried out for use as powder, ground down as ointment or made into potions for drinking. Breasts will be cut off as a source of “mother’s luck” or to be used to attract women to a business. Genitals are taken for virility, fertility and luck. Hands are used to attract customers into a shop; they are often buried under shop doorways as a means of beckoning people in. The eyes give far-sightedness, the tongue makes one a persuasive speaker. Urine and sperm are considered lucky and blood a powerful life force, and so on.

Sello’s hand, therefore, would probably have been ordered by someone starting up a new business. His ear might have gone to a different client with hearing problems, his genitals to someone with impotence or fertility worries and his brain tissue could be eaten to improve intelligence.

All of which may explain why his mother, Salome Chokoe, 39, and his brothers, Nimrod, 16, and 5-year-old Eliphas, were so traumatised when I met them last week. Sello had died the day before — half an hour before I was due to see him — and relatives were gathering around the family’s tiny breeze-block shack with its corrugated iron roof. This is a village blighted by terrible poverty.

“We are all still in shock,” says Salome. She is dressed in a green floral blouse, using a rug as a skirt and a woollen hat to guard against a biting winter wind. “Sello was such a quiet boy, a nice boy who always helped others. He was very bright, always doing his schoolwork at home and always playing little tricks. He was always laughing.

“I just wish that whoever did this to him will be caught and put in prison for life. They must have Satan — demons — inside them. My other boys are terribly traumatised. Now they are frightened to go out.”

But this is all so far away.

Why should it concern us? First, because of the discovery in the Thames of the torso of the boy detectives came to call “Adam”. Secondly, because experts predict that his ritual murder will not be the last we see in Britain. Adam, thought to be aged about 6, has still not been identified. But detective and forensic work has established that he was brought here from Nigeria, a hotbed of black- magic belief, and butchered, probably in a ritual sacrifice aimed at bringing luck to a child-trafficking enterprise.

Analysis of his stomach contents show that he was given a potion containing African calabar beans that would have rendered him paralysed but conscious while he was bled to death, then dismembered. His was a black-magic ritual sacrifice, rather than a strict muti murder, but it was driven by the same beliefs.

Realising the significance of this new kind of murder in the UK, detectives on the case, led by Commander Andy Baker and Detective Chief Inspector Will O’Reilly, refused to bow to pressure to abandon it as being impossible to solve. (An unknown foreign child, no head, teeth or fingerprinting for identification, and dressed only in a pair of orange shorts as a clue. Asked to examine the case, the advice of the Federal Bureau of Investigation in Washington was to drop it.) O’Reilly comments: “Abandoning the case would have sent out the wrong message. Besides, we were the nearest thing this boy had to a family, so we were determined not to let him down.”

The team believe that they now know who killed the boy and hope to bring charges in the near future. “The case has given us a wealth of knowledge we never had before,” says O’Reilly. “And it has told us that while the vast majority of African people are appalled by muti and ritual murder, the migration of cultural beliefs means that such murders are likely to happen again.”

Dr Richard Hoskins, an expert in African and Caribbean cultures at Kings College London, who also advised Scotland Yard in the Adam case, agrees. “In Africa,” he says, “a muti man who is found to have killed to obtain body parts will be hauled up in front of a tribal chief and thrown out of the village.

“The problem in big towns and cities such as London is that communities are dislocated. In small communities in Africa a delinquent muti man could not get away with wrongdoing. Here bad elements can slip in and out of areas anonymously.

“My concern is that without the usual community checks and balances, it isn’t a huge step for them to begin seeking human body parts.”

In areas of London with high African populations, flyers from witchdoctors advertising black magic cures for illnesses, impotence and bad luck are as commonplace as leaflets for takeaway pizza.

Dr Yunes Teinaz, a senior environmental health officer for Hackney council and health adviser to the London Central Mosque (black magic is practised by Muslims and Christians in Africa), is hearing increasing reports of attempts by unscrupulous practitioners to acquire human parts.

“We know that much of the bush-meat trade (illegal imports of meat from African animals) is used in potions and ointments for black magic treatments and we know that other animals are sacrificed for voodoo purposes in the African community,” he says. “But we have a very deep concern over human body parts. We think they could be coming in with the bush meat.”

In Limpopo province, muti murders are not uncommon but the people of Moletjie say that none has happened there before Sello’s. Now parents are afraid to let their children out, in daylight or darkness. But that did not stop several hundred of Sello’s schoolmates gathering last Wednesday for a service at the Komape-Molapo school a mile from his home.

As we arrive, the older children are huddled together, some in tears, while the younger pupils are being sent home.

Mojela Matthews, the principal, says: “This was supposed to be a service to pray for Sello’s recovery. But we have just heard that he has died. We are having to turn it into a memorial service. It is too upsetting for the younger children. They are all terrified. All the children know what happened to this boy — they know about his ear and hand and genitals being taken. They know that these men took some of Sello’ s brain. How do you comfort children at a time like this?” The boy who found Sello, Bernard Ngoepe, an 11-year-old, is brought over but he can’t speak. His eyes are wide, his lips trembling. The school has asked for a counsellor to come from the nearest big town, Pietersburg, to help the boy.

“He’s been in trauma ever since he found Sello,” says one of the teachers. “He saw Sello repeatedly trying to stand up, in spite of his injuries. That sight will probably haunt Bernard for ever.”

Back at Sello’s home, the undertaker has arrived, not with a coffin but with a flatbed truck loaded with chairs as villagers and relatives arrive to pay their respects. Each one appears in shock. Occasionally, one is led away in tears, yet Salome Chokoe’s eyes are dry. “I just can’t take it in,” she says.

They buried Sello at the weekend. And as they lowered him down, they must surely have been thinking of another burial, perhaps in a more prosperous part of the province, as a wealthier person, bereft of sympathy or understanding, took the boy’s hand and put it in a hole under the doorway of a shiny new shop.