Sri Lanka's civil war ended with "credible" evidence that war crimes were committed. Now Channel 4 News can reveal mounting evidence that the government is still torturing Tamil prisoners.

Please wait while this video loads. If it doesn't load after a few seconds you may need to have Adobe Flash installed.

The UN has already found that evidence of the killing of up to 40,000 civilians amid allegations of serious human rights abuses amounted to "credible allegations" that war crimes had been committed during the last days of the civil war in 2009.

Now ahead of a United Nations meeting tomorrow, human rights groups are calling for an urgent investigation into the allegations that human rights abuses are still rife in Sri Lanka.

President Mahinda Rajapaksa's government dismisses all that as "preposterous". He has embarked on a charm offensive to help repair his island nation's tarnished reputation.

But Channel 4 News has spoken to two men who say that behind the smiles, there still lies a vengeful, sadistic regime.

The Tamil Tigers stand accused of war crimes too. Suspected fighters were rounded up at the end of the war, but it is claimed suspects are still being detained - and tortured - today.

'It felt like I was breathing fire'

"Nimal", whose identity we have concealed, claims he was tortured by Sri Lankan security forces in June this year because of his association with the Tamil Tigers.

"They used to beat me with a steel cable. It would peel away my skin. The pain would be simply unbearable. They would hang me upside down and dunk my head into water. They covered my head with a polythene bag soaked in petrol and tied it tightly round my neck. When I tried to breathe in it felt like I was breathing in fire," Nimal tells me.

They would tie me upside down and dip me into a barrel of water. 'Nimal'

"I had no medical treatment. I couldn't sleep because I had to lie face down so I wasn't laying on my wounds. You can't sleep in that much pain. They would tie me upside down and dip me into a barrel of water.

"My wounds would feel like they were burning as soon as they touched the water. When I screamed in pain they would come back with the confession and try again to make me sign it," he continues.

"Maaran" says his treatment at the hands of the government made him want to die.

"They hung me upside down and shoved my head in a barrel of water. They laid me face down on a table and hammered me with wires, poles and rods. They burned me with cigarette butts and when I asked for water to drink they gave me urine. I thought it would have been better if I died at the end of the war rather than to have survived to face this."

The men I met have now been granted asylum in the UK. Both had past associations with the outlawed Tamil Tigers. Both were tortured in Sri Lanka this summer.

It can take years to be granted asylum. The two men I met were approved within weeks because the government accepted their stories. Both had past associations with the outlawed Tamil Tigers.

Channel 4 News can reveal mounting evidence that the government is still torturing Tamil prisoners.

Calls for 'urgent investigation'

"Nimal" and "Maaran" are not alone. Tomorrow a United Nations committee meets to consider mounting evidence that Sri Lanka is in breach of the UN convention against torture, to which it is legally bound.

Among reports submitted to this committee from 12 international organisations, the most detailed and damning is from the UK-based group Freedom from Torture.

Sri Lanka seem to have employed the full range, pretty much, of torture methods. Juliet Cohen, Freedom from Torture

Its Sri Lankan caseload is based on forensic medical documents compiled from 35 men and women, tortured, it says, since the end of Sri Lanka's civil war. It says torture perpetrated by the military and the police is still occuring in 2011.

The evidence, the group concludes, is sufficiently serious to merit urgent investigation.

Juliet Cohen of Freedom from Torture, says the effects of torture can last for years.

"People have been through overwhelmingly terrifying experiences, and these in Sri Lanka seem to have employed the full range, pretty much, of torture methods.

"People seem to be having a very high concentration of torture within quite a short time frame, and they're very damaged by it and theyve got physical and psychological scars."

Turned back

This year, the British government has forcibly removed an unknown number of failed Tamil asylum-seekers to Sri Lanka.

The UK has signed the UN convention against torture, which states that no-one should be deported if there are "substantial grounds" to believe they would be tortured.

The government bases its assessment of that risk on the UK Border Agency's country of origin information reports.

The latest COI report on Sri Lanka is dated July this year. Under the section on torture, it quotes international human rights groups, other governments and the UN as stating that torture is still rife in Sri Lanka.

Having said all that, the report then cites a letter, in paragraph 8.35, from a British diplomat - our man in Colombo - who writes: "I asked the Senior Government Intelligence officials if there was any truth in allegations that the Sri Lankan authorities were torturing suspects. They denied this was the case."

The Border Agency told us that it only returns those whom they are satisfied are not at risk, in line, it says, with a European court ruling that not all Tamil asylum-seekers do require protection.

Human rights groups contend that failed Tamil asylum-seekers are all at risk.

From the evidence we have heard from those who have made it out of Sri Lanka's torture camps, the long war is not over yet.