As the ancient practice of slavery continues to haunt Sudan, Western charities are resorting to desperate measures to rescue the slaves - triggering a fierce debate.

Listen to Mike William's report

Christian Solidarity Worldwide is one of a number of organisations who give cash to people to buy back their enslaved relatives, captured in the largely Christian south by northern militia groups.

Each 'redemption' scheme costs between $50 to $100.

Reverend Stuart Windsor, UK Director of Christian Solidarity Worldwide told the BBC that over the last 18 months, "we've redeemed about 1,200 women and children from slavery".

Fear of increased slavery

But there are those who fear that the programme of redemption exposes others to attacks from the slave traders.

Many point out that the numbers of slaves being bought back in Sudan have increased to thousands in the past few years. The money for their release comes from well-meaning people in the west, who raise thousands of dollars.

"They are paying money for the freedom of a person. For us that is ethically wrong, you cannot buy somebody's freedom," said Patrick McCormick, a spokesman for the United Nation's Children's Fund (Unicef).

"We find it hard to believe that it hasn't encouraged people, if they are desperate, to sell their children. Or else, encourage slave traders to increase their business," he said.

Dilemma

Unicef is highly critical of the redemption schemes. But the UN agency has itself come in for criticism for an earlier programme in India, where it gave cash to heavily indebted mothers to stop them selling their children into bonded labour.

Unicef denies any similarity in the cases, but it illustrates how difficult is the dilemma. The fee is not much to buy the freedom of a human, particularly if all other avenues are dead.

Mike Dotteridge, the Director of Anti-Slavery International, does not approve of redemption but understands the motives of those who do.

"It's been very frustrating. There seemed to be no progress whatsoever and therefore no alternative to this system of ransoming. But as soon as you introduce money, there are uncontrolled side effects," Mr Dotteridge said.

"The money is either used to buy more slaves or it goes into other people's pockets. It reinforces the power of a exploitative hierarchy, it goes into the arms trade and so on," he said.

Wide support

The groups who buy back slaves are not radical fringe organisations. Christian Solidarity Worldwide has as its president Baroness Cox - a former deputy speaker of the UK parliament's House of Lords.

Several other British peers and half a dozen MPs sit on its various governing bodies. Churches across the UK fund its activities and it claims to have 20,000 supporters across the country.

The Anti-Slavery Group in the US has had school children donate pocket-money and Congressmen voicing support.

"In the American struggle for freedom here abolitionists brought back slaves. So we've had this debate and it's been settled 150 years ago," said Dr Charles Jacob, the group's president.

Though it is easy to condemn the redemption programme, to offer an alternative solution is much harder.

Those who buy freedom say they do understand that peace and justice in Sudan would bring an end to the trade in humans.