The report into arbitrary detention, prison conditions, the Vavuniya riot, and its aftermath published by the Sri Lankan Campaign for Peace and Justice documents the island's human rights abuses and examines the treatment of detainees in the wake of a riot in the country's Vavuniya detention centre last June, that triggered brutal police retribution.

It found that prisoners from the riot were kept in "abominable conditions and deprived of basic human rights". One case study documents the treatment of Ganesan Nimalaruban, an aspiring post office worker who was arrested in 2009 and subjected to three days of torture that left him with heart and respiratory problems, the report says. He later died in custody.

Nimalaruban's family said their 28-year-old son was beaten regularly in prison and required frequent visits to hospital where, shackled on the floor and denied food and water, he also contracted dengue fever. Authorities claim Nimalaruban suffered a fatal heart attack because of the riot.

His mother, Rajeswari, insists her son died because of repeated beatings that police have attempted to cover up. She says her family, left impoverished by Nimalaruban's legal battle, has also been subjected to intimidation.

Another case study describes the ordeal of an artist, identified as MM, who was arrested in 2007. The 28-year-old, who has suffered from polio since childhood, claims he was forced after days of torture into signing a false confession stating he had assisted Tamil Tiger rebels.

He said he had his toenails extracted and was then electrocuted, rendering him unconscious for three days. Now convicted, he has been sent to prison in the central city of Kandy, far from his home in the north. He has barely been permitted contact with his wife or son, who was born just months after his arrest.

The report also criticises a government rehabilitation programme for former Tamil Tiger soldiers that, it says, is also blighted by violence and, despite officially being classed as voluntary, is frequently used as a tool to prolong detention without trial.

The Sri Lanka Campaign report says the treatment of Tamil prisoners has, along with other human rights violations, been largely unnoticed by an outside world eager to believe that the country's recent conflict is consigned to history.

Fred Carver, campaign director, said: "The report is an important reminder that not only were atrocities and war crimes committed on a large scale by both sides during the war but torture, arbitrary imprisonment and other human rights abuses continue on a large scale in Sri Lanka.

This report was undertaken by Tamil and Sinhalese researchers from Sri Lanka and the United Kingdom. The final manuscript was produced by the Sri Lanka Campaign for Peace and Justice.