At the age of 21, Sivatharsan Sivakumaravel is preparing to die. Lying under layers of damp duvets and surrounded by passionate and at times tearful supporters, Mr Sivakumaravel is one of two young Tamil men who have vowed to starve themselves to death outside the Houses of Parliament unless Britain forces the Sri Lankan government to call an immediate ceasefire in its war with Tamil Tiger rebels.

Mr Sivakumaravel should be like any other university fresher, enjoying the carefree existence of a first-year student. His family fled Sri Lanka eight years ago, settled in Mitcham in Surrey, and have pushed their three sons to earn themselves a university degree and to try to forget about the three decades of conflict that have blighted their homeland.

But instead of studying for upcoming exams, or exploring the town with his new university friends, Mr Sivakumaravel is voluntarily fasting to death.

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The computer science student and his Sri Lankan university friend Parameswarn Subramaniyan, 28, have both been refusing food and water since 10am on Tuesday in protest at what they say is the international community's inaction over the ongoing conflict in their homeland.

They have signed statements saying they will refuse any medical assistance until their demands are met and are already in poor health because of dehydration. Speaking to The Independent from his makeshift bed in Parliament Square a tired and weakening Mr Sivakumaravel said he would continue his hunger strike even if the police or paramedics tried to remove him. "My mother keeps phoning me, telling me to stop this protest but I will not eat or drink anything until we have a ceasefire," he said yesterday. "The world has ignored the Tamil people for too long. My wish is that we will be the last two Tamil deaths because of this war."

What began as a spontaneous protest by thousands of Tamils who blockaded Westminster Bridge on Monday evening has since transformed into a solemn night and day demonstration in which two young men have effectively resigned themselves to death.

Their demands are almost impossible to meet. As well as an immediate ceasefire in Sri Lanka, the two men are asking for the UN secretary general Ban Ki-moon and Gordon Brown to meet them and for Britain to remove the Liberation Tigers of Tamil Eelam from its list of proscribed terrorist organisations. Downing Street last night had no comment.

It is difficult to tell whether the two men are seriously prepared to die for their cause but a recent spate of publicity suicides among the Tamil disapora shows the community is more than willing to sacrifice themselves.

Last month thousands of Tamils attended the funeral of Murugathasan Varnakulasingham, a 26-year-old computing graduate from north London, who set himself on fire outside the UN building in Geneva. A week later another Tamil man tried and failed to self-immolate outside Downing Street.

In India and Malaysia at least six Tamils have set themselves alight in the past two months. But this latest expression among Britain's Tamils to sacrifice themselves is now being carried out in the heart of London and raises the astonishing prospect of two men dying on the doorsteps of Parliament.

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Mr Subramaniyan, the second hunger striker, was too tired to talk in detail yesterday but he has said six members of his family were recently killed in fighting between the Sri Lankan army and Tamil Tiger rebels. His claims are impossible to verify because the Sri Lankan government has banned journalists from the war zone. Mr Sivakumaravel says he has not heard for weeks from his relatives who live in the Vanni area, where thousands of civilians are thought to be trapped.

Because both men have refused to even drink water, medical experts are concerned that their health could rapidly deteriorate. Yesterday afternoon paramedics tried to persuade them to go to hospital but both men refused.

Last night a spokesperson for London Ambulance Service said they had placed an ambulance on 24-hour alert. Three doctors from within the Tamil community, meanwhile, are taking it in turns to monitor the pair.

Inthu Kumarendran, a 44-year-old doctor who was on the day shift yesterday, said hunger strikers who refuse both food and water can die in as little as 10 days. "I'm particularly worried about renal failure," she said. "They hardly passed any urine yesterday and they are getting very bad headaches. Some people may be horrified by what they are doing but in our culture fasting is something that is very much respected. Tamils have often chosen to starve themselves to death in protest at what is happening."

Many supporters compared the two men's protest to that of Lieutenant-Colonel Theleepan, a Tamil Tiger commander who is venerated for fasting to death in 1987. Although the UK has proscribed the Tamil Tigers as a terrorist organisation because of their indiscriminate targeting of civilians and their pioneering of suicide bombs, the majority of Tamils look upon the Tigers as freedom fighters and see them as the only group that can stop their half of the island being overrun by the Sinhalese. Many of the chants at this week's protest have praised Vellupillai Prabhakaran, the leader of the Tamil Tigers.

Earlier in the week police snatch squads tried to confiscate Tamil nationalist flags under the Terrorism Act, a tactic which led to scuffles with the crowd. But yesterday afternoon it appeared the police were largely content to leave the flags in place.

As more Tamils came from their jobs to gather outside Parliament Square late yesterday, the two hunger strikers expressed concerns that they might be forgotten by Britain's political elite over the Easter period. "I don't know what will happen but I hope they are listening," said Mr Sivakumaravel, slowly raising a finger to point to Parliament. "All we are asking is for Britain to begin treating Tamils like human beings. They must do something, because it seems no one else will."

Hunger strikes: Two weeks to live

*A hunger strike where a protester refuses even to drink water can cause medical problems very quickly. Without carbohydrates the body uses natural stores of glucose, then fatty deposits, and finally muscles, organs and bone marrow. Without water a protester can die in less than two weeks. A 5 per cent loss in body fluid can mean irreversible liver damage; a 10 per cent loss is usually fatal.