Watch Richard Galpin's report

On an ordinary weekday at the shrine of Shah Dola in the Punjabi city of Gujrat, hundreds of worshippers come to celebrate the life of one of Pakistan's most revered Sufi saints.

Some choose to show their respect by dancing wildly - in a state of ecstasy.

Women unable to conceive come to pray at the temple

By the tomb itself dozens of women pray intensely. By doing so, they believe, they will be blessed with a child.

According to a legend dating back hundreds of years a woman who's unable to conceive will become fertile by offering prayers here. But at a price.

The couple can expect their first-born to be handicapped - a rat child with a tiny head. And it must be handed over to the shrine.

The legend is very much alive. One woman, who had come to pray for a son, said God would punish anyone who did not honour their commitment.

Deliberately deformed

"Rat children" grow up with mental and physical handicaps

Experts say they are being deliberately deformed by criminal gangs operating around the shrine who then use them for begging.

Many of the children handed over to the shrine or those claiming to represent it end up on the streets.

At the main bus-stand in Gujrat we quickly came across a group of several rat-children with their owners.

They all have the distinctive shrunken heads; they're severely handicapped and can't even speak.

With their owners close behind, they approach passengers sitting in their minibuses waiting to leave. They demand money and they get it.

High value beggars

It is widely believed that the handicapped are closer to god

It is widely believed that the handicapped are closer to God and must not be ignored. Their value as beggars is therefore enormous.

Anusheh Hussain, head of Sahil, an organisation fighting against child exploitation in Pakistan says the rat-children can be sold for large sums of money:

"One has heard that these children are sold from anywhere between 40,000 - which is approximately 10 dollars - to 80,000 rupees per child" she says. "On average they will be able to make, through begging, around 400 to 500 rupees a day, which makes it a very lucrative business considering that's twice the amount a civil servant makes."

Healthy babies

There is suspicion that healthy babies are deformed and sold for begging

Because of this there is deep suspicion that the legend of Shah Dola has in fact been fabricated to trick ordinary people into handing over perfectly healthy babies. It's believed these are then deliberately deformed so that they can then be sold for begging.

Pirzada Imtiaz Syed, a trade union leader based in Gujrat, he says he has heard of many cases of abuse:

"I have not seen this myself but I have heard from many people that they use iron rings which are placed on the baby's head to stop it growing. I believe there are about 10,000 rat children in Pakistan controlled by a mafia of beggars who are all over the country. These children are also physically and sexually abused."

Medieval contraptions

The allegation that the children are being deformed using medieval contraptions is of course denied by those associated with the shrine in Gujrat. They say the rat-children are suffering from a genetic disease.

Dr Qasim Mehdi: theories of genetic disease are medically impossible

But Pakistan's top genetic scientist, Dr Qasim Mehdi, who investigated this for three years, says this is medically impossible.

"In order for a disease to be genetically inherited you have to have a disease running in the family" he says.

"The point is that these children are not related to one another by any stretch of the imagination. Our investigation shows that they come from very different backgrounds, from very different families. So if there is no blood relationship between any two individuals and between even an incident where a father or son or uncle was involved, it cannot be a genetically inherited disease."

'Crime against humanity'

The government says it is very concerned but claims that, following action by the authorities in the 1980s, the gangs operating at the shrine were removed and there are now no children being deliberately deformed in this way.

The government says children are no longer being deliberately deformed

But we found otherwise. At the bus-stand in Gujrat there was one rat-child being used for begging who looked at most seven or eight years-old. The minister responsible, Raja Zafar-ul-Haq promised further government action.

"We will certainly go after these people" he says, "they are criminals and if you can give me any idea as to their whereabouts then we can ask the police to investigate. It's a crime against humanity."