A failed asylum-seeker who returned to Darfur under a government repatriation scheme has been murdered by Sudanese security officers after they followed him home from the airport in Khartoum, The Independent has learnt.

Adam Osman Mohammed, 32, was gunned down in his home in front of his wife and four-year-old son just days after arriving in his village in south Darfur.

The case is to be used by asylum campaigners to counter Home Office attempts to lift the ban on the removal and deportation to Sudan of failed asylum-seekers. Next month, government lawyers are expected to go to court to argue that it is safe to return as many as 3,000 people to Khartoum.

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But lawyers for the campaigners will tell the Asylum and Immigration Tribunal that people who are returned to Sudan face imprisonment, torture and death. Mr Mohammed, a non-Arab Darfuri, came to Britain in 2005 seeking sanctuary from persecution in Sudan, where he said his life was in danger. The village where he was a farmer had been raided twice by the Janjaweed, the ethnic Arab militia, forcing him and his wife and child to flee their home.

His family in Britain told The Independent that Mr Mohammed witnessed many villagers being killed and became separated from his wife during a second attack on the village a few weeks later. He escaped to Chad before making his way to the UK in 2005.

But last year his appeal for asylum was finally turned down and he was told that he faced deportation. In August last year he was flown to Khartoum under the Home Office's assisted voluntary return programme, in which refugees are paid to go back to their country of origin. He stayed in Khartoum for a few months and then, when he believed it was safe, he travelled to Darfur to be reunited with his family.

Mohamed Elzaki Obubeker, Mr Mohammed's cousin and chairman of the Darfur Union in the UK, said: "The government security forces had followed him to another village, Calgoo, where his wife and child had sought help. They came to the village to find him and then targeted him. They shot him in front of his wife and son."

Waging Peace, the human rights campaign group which is to bring Mr Mohammed's case to the attention of the Asylum and Immigration Tribunal in April, said it deplored any attempt to lift the ban on returning non-Arab Darfuris to Sudan. Louise Roland-Gosselin, the group's director, said: "We are deeply concerned by what has happened to Adam and many like him.

"The Government still wants to send back Darfuri asylum-seekers. But it is difficult to understand on what basis the Government is making this decision. The International Criminal Court has issued a warrant for the arrest of Sudan's President, Omar al-Bashir, over murders committed during the genocide. It shows just how out of touch the Home Office is with the reality taking place in Khartoum if it thinks it's safe to send people back to a country where there is clear evidence of genocide."

Amnesty International's UK refugee programme director, Jan Shaw, said yesterday: "Darfur is still incredibly dangerous. A climate of insecurity prevails and human rights abusers act with impunity. Women are still exposed to rape and other civilians are still being murdered or forced to flee their homes. Even in Khartoum we have concerns that Darfuris may be at risk of persecution. No one should be removed to Sudan at the present time.

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"The UK should also treat refused asylum-seekers humanely when they have come to the UK seeking sanctuary. People from Sudan have been refused asylum here, but at present they can't be removed. Yet in most cases this means that all their support is cut off and they could be left destitute on the streets with nothing. It's tragic if some people then get so desperate that they return to Sudan despite the risks to their safety."

Between 2,000 and 3,000 Darfuris living in the United Kingdom are at risk of removal to Sudan.

Mr Obubeker added: "The government suspects everyone who returns from the United Kingdom as being anti-government, whether it is true or not. They regard them as enemies of the state. What happened to my cousin is a terrible thing to have happened to someone who thought he had escaped to a country for safety. He wanted to live in Britain because he knew it was too dangerous for him to live in Darfur. But despite making claims for asylum, his case was rejected. He became even more sad when he found out that his asylum case was lost.

"He hadn't made many friends in Birmingham and he started to think about his wife and son. It is a tragedy because all he wanted was a new life in this country – and for that he is dead."

Mr Mohammed spent most of his time in Britain living in Perry Barr, Birmingham, where his family said he found it difficult to integrate with the community.

Home Office guidance for caseworkers deciding asylum claims brought by Darfuris makes it clear that the Government believes it is safe to return people to Khartoum. The guidance states: "The fact that a returnee has unsuccessfully sought international protection in the United Kingdom is likely to be known to the Sudanese authorities... However, a person will not as such be at real risk on return to Khartoum, either at the airport or subsequently, simply because he or she is an involuntary returnee of Sudanese nationality."

A UK Border Agency spokesman said: "We consider every asylum application with the utmost care and, crucially, there is oversight from the independent courts. We are continuing to monitor the situation in Sudan, and in July last year we took the decision to stop returning non-Arab Darfuris until the courts decided it was safe to do so."

Trouble spots: Voluntary returns

Afghanistan

Britain stopped deporting Afghan refugees in 1995 – failed asylum-seekers were granted "exceptional leave to remain". The rules changed after the 2001 invasion of Afghanistan and end of Taliban rule; a voluntary assisted return programme began in 2003 and single claimants were offered £600 to go back.

Iraq

Iraqis went back to northern Iraq under the voluntary scheme from 2003 and have been offered deals to go back to Baghdad. Under the terms, those returning to Iraq sign a waiver releasing the International Organisation for Migration from any responsibility for or liability towards them.

Zimbabwe

In 2006, 200 failed asylum-seekers voluntarily returned to Zimbabwe. Last year, the Government stopped forced returns but Zimbabweans can still take advantage of the voluntary programme to return.