The case of Dr Musa Saadeldin - who was detained and tortured by Sudanese security police - exposes the chaos in Britain's asylum system that was exploited by the convicted ricin plotter Kamel Bourgass.

But while Bourgass passed through the holes in the creaking system to stay in Britain illegally, Dr Saadeldin's attempts to find a haven from persecution have fallen on deaf ears.

Dr Saadeldin left behind his wife and parents, after being tortured for providing medical assistance to the victims of government and militia attacks.

He and his supporters in Britain say he has received no sympathy from the UK authorities. He was told he should have stopped treating rebel victims and should have returned to Khartoum if he thought his life was in danger in Darfur.

On Tuesday this week, Jack Straw, the Foreign Secretary, categorised the killing in Darfur, where at least 300,000 have died, as genocide.

And last week he said: "There are still members of the so-called international community, members of the Security Council and others, who are turning a blind eye to clear atrocities which have taken place in Darfur."

Despite those assertions, Dr Saadeldin has received no sympathy from the UK authorities. Now the case has been taken up by politicians and a fresh appeal against the decision is planned. But his supporters say his case is only the tip of the iceberg, with dozens of other Sudanese refugees facing deportation back to persecution in Darfur.

On Wednesday Mr Straw said: "Obviously, I do not know about this particular case, but our asylum system and process is most careful about the claims people make, and quite rightly so. Whilst it is the case that most asylum claims are unfounded, some 20 per cent are well founded, and you don't know which ones are well founded until they are assessed.

"It is a very careful process. I do not know [of] anybody who was returned when they were at risk."

A supporter of Dr Saadeldin's appeal is Peter Verney, a Sudan specialist and adviser to the Darfur investigation by the Commons international development committee.

Mr Verney said: "It sums up all that's wrong with our approach to asylum, that a doctor from Darfur, as patently honest as this, with such a shattering story, could be turned down. If he'd been a British Save the Children worker in Darfur, as I was in the 1980s, he'd be regarded as heroic.

"Dozens of Darfur refugees in the UK are being told it's safe for them to return to Khartoum, as if Darfur were just a local tribal affair. It's not; it's part of a country-wide problem created by the Sudanese dictatorship.

"By refusing asylum to people like this doctor, we're not just being mean and petty. We're sending a message to the regime that they can carry on with the slaughter."

Dr James Smith, the chief executive of the Aegis Trust, which co-ordinates the anti-genocide Protect Darfur campaign, said telling Dr Saadeldin to move to Khartoum was "rather like telling a Jew who has managed to get to Britain during the Holocaust that they will be fine going back to Berlin because the extermination camps are only in Poland."

Dr Saadeldin was a manager and doctor at Umm Kedada hospital in northern Darfur until March last year.

After witnessing the consequences of the campaign of ethnic cleansing launched against the black African farmers of his Zaghawa tribe, he began to help the anti-government Sudan Liberation Army (SLA) and provided them with medical supplies.

He also treated those injured in the attacks, regardless of which side they were on.

He was picked up by security police and interrogated.

"They tortured me and beat me and told me I was a slave," he said. "They threatened to kill me."

He refused to confess to any crime and was eventually released, but was kept under surveillance. Last March, as he met other SLA supporters, police arrived to carry out a raid. He describes escaping over a wall and running 25km to a friend's house, where he borrowed money and made his way to Port Sudan, on the east coast. There he boarded a ship for Britain and entered the country hidden in the back of a lorry.

He got out in Birmingham and presented himself to the authorities to claim asylum. After a hearing on 6 June last year, the Home Office wrote to Dr Saadeldin on 17 June dismissing his account.

Of his escape from the police raid, the Home Office said: "If the security forces raided the house as claimed, they would have positioned men on the outside of the house near all exit points." And it maintained that if his fear of persecution had been genuine, he "would have left Sudan at the earliest opportunity".

He appealed against the decision, but on 24 August the adjudicator again rejected his claim, arguing that he could have moved to another part of Sudan if he feared for his safety. His supporters are putting together a new case and are optimistic they can persuade the Home Office to change its mind. Since his application and appeal were rejected, he has been living in the north of England.