By Megan Lane and Brian Wheeler BBC News Online Magazine

Anyone who has experienced this desire [for sleep] knows that not even hunger and thirst are comparable with it Menachem Begin, who was tortured by the KGB

Hallucinations, paranoia, disorientation - these are some of the symptoms of sleeplessness endured by the contestants on Channel 4's reality TV show Shattered. The 10 participants are starving themselves of sleep for a week in the hope of winning £100,000.

The channel has vigorously denied claims that it is exploiting its contestants, and has safeguarded their welfare by using ethics and medical advisors.

But on leaving the show, contestant Craig North said: "It was like torture being deprived of sleep. It's not every day you try to spend 180 hours without any sleep."

Sleep deprivation is not like torture - it is a form of torture, a tactic favoured by the KGB and the Japanese in PoW camps in World War Two.

The British Army was also accused of using sleep deprivation to extract information from suspected IRA members in 1971.

"It is such a standard form of torture that basically everybody has used it at one time or another," says Andrew Hogg, of the Medical Foundation for the Care of Victims of Torture.

Psychosis

Going without sleep is intensely stressful, with unpredictable short and long-term effects. People lose the ability to act and think coherently. And as it leaves no physical mark on the victim, the interrogator can claim that they never laid a finger on those in their charge.

Former KGB prison in Vilnius, Lithuania

John Schlapobersky, consultant psychotherapist to the Medical Foundation for Victims of Torture, was himself tortured through sleep deprivation, in his case in apartheid South Africa in the 1960s.

"Making a programme in which people are deprived of sleep is like treating them with medication that will make them psychotic. It also demeans the experiences of those who have involuntarily gone through this form of torture. It is the equivalent of bear-baiting, and we banned that centuries ago.

"I was kept without sleep for a week in all. I can remember the details of the experience, although it took place 35 years ago. After two nights without sleep, the hallucinations start, and after three nights, people are having dreams while fairly awake, which is a form of psychosis.

"By the week's end, people lose their orientation in place and time - the people you're speaking to become people from your past; a window might become a view of the sea seen in your younger days. To deprive someone of sleep is to tamper with their equilibrium and their sanity."

KGB interrogation

Former Lithuanian freedom fighter and political prisoner Juozas Aleksiejunas was tortured with sleep deprivation by the KGB, just after the end of WWII.

He was arrested for being a member of Lithuania's anti-Soviet partisan movement, which fought a guerrilla-style war against the USSR between 1944 and 1953.

The KGB questioned him for three nights in succession and prevented him from sleeping during the day.

"It is difficult to think when there is no sleep. Human beings can almost lose consciousness because of it," he says.

Mr Alekseijunas, who is now a pensioner and a former guide at a Lithuania's Museum of Genocide Victims in Vilnius, laughs when asked what sleep deprivation does to the mind.

"Try yourself to eat only 300g of bread, the daily ration we got in prison, during two months and after it not sleep for three days and nights.

"The desire to have some sleep was the only thing which I was dreaming about."

Guantanamo Bay

Sarah Green, of Amnesty International, says claims of this type of torture have increased in the past couple of years.

Guantanamo Bay has been the focus of concern

"It is alleged that the Americans have used it in Guantanamo Bay and Iraq," says.

The Pentagon has denied torturing Iraqi prisoners, but it has admitted using sleep deprivation and playing loud rock music to break prisoners' resistance.

Ms Green says that other countries alleged to use sleep deprivation are China, Saudi Arabia - the British men accused of bomb attacks and imprisoned for two years say they were tortured in this way; the Saudis deny it - and Israel.

There, the Landau Commission in 1987 concluded that "non-violent psychological pressure" could be used in questioning prisoners who had information that could prevent terror attacks. Twelve years later, the Israeli Supreme Court effectively revoked this permission.

'Uninterrupted sleep'

Menachem Begin, the Israeli prime minister from 1977-83, was tortured by the KGB as a young man. In his book, White Nights: The Story of a Prisoner in Russia, he wrote of losing the will to resist when deprived of sleep.

"In the head of the interrogated prisoner, a haze begins to form. His spirit is wearied to death, his legs are unsteady, and he has one sole desire: to sleep... Anyone who has experienced this desire knows that not even hunger and thirst are comparable with it.

"I came across prisoners who signed what they were ordered to sign, only to get what the interrogator promised them.

"He did not promise them their liberty; he did not promise them food to sate themselves. He promised them - if they signed - uninterrupted sleep! And, having signed, there was nothing in the world that could move them to risk again such nights and such days."