India: The deadliest heatwave to hit India for more than 100 years has killed more than 2,500 people as temperatures soared to 50C and even the roads melted. But even among so many deaths, the murder of Thepa Kharia stands out.

A few weeks ago neighbours of the 55-year-old labourer found his body in a pool of blood at his home in an isolated village

280 miles west of Calcutta

And it was only his body – his head had been hacked off by an occult group called the Orkas, who buried it in a parched ­farmer’s field in a bloody ritual meant to summon the rain and save their shrivelling crops.

Days later the annual monsoon finally reached the southern tip of India. Then the rain worked its way slowly across the country, chasing away the searing heat.

But the downpour will not wash away the stain left by Thepa’s murder. His death has exposed a sick superstition that simmers beneath the surface in remote parts of India and has now boiled over in the searing heat.

Human sacrifice, for years assumed to live on only in fictional works like horror film The Wicker Man, is in fact alive and well in the 21st century. One case was even recorded right here in Britain as recently as 2001.

When the torso of a five-year-old boy was found floating in the River Thames near Shakespeare’s Globe, police found that his head, arms and legs had been cut cleanly off and what remained of his body had been entirely drained of blood.

The main clue to his fate came when a lab report showed his intestine contained traces of the African calabar bean, a powerful poison used by adherents of voodoo. This creates paralysis without any anaesthetic effect, meaning the victim would have felt every cut of the knife in a sickening ritual.

He was named as Adam by officers in the case, who also released a photo of a Nigerian boy they believed might be him. But his identity was never confirmed and his killers were never caught.

Human sacrifice is far more common in countries like India where a minority of tantric shamans still promote it to gullible communities of uneducated peasants.

Best known in the West as techniques to prolong and ­intensify sexual pleasure, in remote areas tantric rituals loosely derived from the Hindu faith can also include animal, and, in extreme cases, human sacrifice to please the gods and guarantee good luck.

It is so widespread that in 2006 there were 28 cases of human sacrifice in just four months in the northern province of

Uttar Pradesh

In one particularly gruesome example one couple were so desperate for a son they consulted a local shaman.

On his advice Madan and Murti Simaru kidnapped six-year-old Mona Kumar from a neighbouring family, took him to a river bank and mutilated his body as the priest chanted over them. Then they killed the boy and washed themselves in his blood to complete the fertility ritual.

In May this year a “tantric sorcerer” was lynched after he beheaded five-year-old Sanatan Bag in front of his parents on a tea plantation in the north-eastern state of Assam. And in the south-eastern province of Andhra Pradesh a boy of 14 was abducted by a sect searching for hidden treasure in 2012.

They took him to an abandoned fort and slaughtered him under a new moon, believing that this would please ancients spirits who would then show them how to find the treasure.

Later the same year a man sacrificed his own wife in the hope of a bountiful harvest.

And in 2011 a seven-year-old girl Lalita Tati was murdered and her liver cut out as an offering to the Hindu goddess Durga by two farmers hoping for a better crop.

Indian police officer AK Singh, who has investigated many human sacrifices, reveals: “It’s often an open-and-shut case. It isn’t difficult to get confessions.

“Normally the villagers or the families of the victims do that for us. But there is little we can doto stop it. These people are living in the dark ages.”

Human sacrifice also continues across the border in Bangladesh. In 2010 a brickmaker was arrested for killing one of his labourers and pouring the blood on his field to improve the quality of his mud bricks.

On the opposite side of the planet in Mexico, human sacrifice is usually associated with the ancient Aztec civilization, where priests would cut out the still-beating heart of a victim at the top of a pyramid.

But three years ago a sickening triple murder raised fears that a similar ritual is making a comeback. Eight members of one family were charged with kidnapping and murdering two boys aged 10 and a woman of 55 in the copper mining town of Nacozari a few miles from the US border. The victims had been sacrificed to Santa Muerte (Saint Death), a rapidly growing cult in Mexico which is popular with drug smugglers and cartel hitmen. The victims’ throats and wrists had been slashed so the blood could be collected and spread on a sacrificial altar.

Two of the bodies were buried near the family’s home, but one of the boys was buried in the dirt floor of their shack.

Andrew Chesnut, chairman of Catholic studies at Virginia Commonwealth University, says there have been other recent reports of human sacrifice in Mexico. He said: “With no clerical authority to stop them, some practitioners engage in abhorrent rituals.”

But the real hotbed of human ­sacrifice is Africa, where poor or ­disabled women and children can be hunted down and sold to witch doctors who sacrifice them then “harvest” the body parts. In Tanzania, hunters target albinos born with snow-white skin, blond hair, and blue eyes.

Widely regarded as devils, they are ­regularly blamed for natural ­tragedies such as deaths and droughts.

However, their organs are used to make charms or potions that are used in medicine meant to lift curses or to bring great riches.

In many cases the victims are carved up while they are still alive to make the potions “more potent”.

Angel Salvatory, 19, had to run for her life when a gang led by her own father attacked her. She had spent her teenage years at the Kabanga Protection Centre, a government safe house for albinos. Her mother Bestida Simon said: “Her father thought she was a gift from God he could use to get riches. He had wanted to attack her since she was three months old.”

Across the continent in Uganda it’s not just albino children at risk. The charity KidsRights believes hundreds of children have been murdered in recent years by a network of witch doctors who have turned human sacrifice into a lucrative business.

Children are chosen because their purity and innocence is supposed to make the sacrifice all the more potent. The government has formed a task-force to tackle the epidemic, but campaigners say the new body has underestimated the scale of the problem and is not bringing enough killers to justice.

KidsRights spokeswoman Lydia van der Putten said: “In many of these cases, body parts were removed by witch doctors when the children were still alive.

“Such sacrificial rituals, and the subsequent wearing, burying or eating of a child’s body parts, are thought to bring business success, personal prosperity and health.”

Polino Angela, an ex-witch-doctor who now campaigns against human sacrifice, claims to have killed 70 people. He says he was initiated at a ceremony in Kenya, where a boy of 13 was sacrificed. He said: “The child was cut with a knife and from the neck down was ripped open, then put on me.”

He even claims to have sacrificed his own 10-year-old son on his bosses’ orders.

He said: “I deceived my wife and made sure that everyone else had gone away and I was with my child alone. Once he was placed down on the ground I used a big knife and brought it down like a guillotine.”

With more reports from Nigeria, Liberia, South Africa, Namibia and Zimbabwe, there are fears human sacrifice is spreading.

It seems these dark and terrifying rituals are anything but a dying art.