When Elif's father told her she had to kill herself in order to spare him from a prison sentence for her murder, she considered it long and hard. "I loved my father so much, I was ready to commit suicide for him even though I hadn't done anything wrong," the 18-year-old said. "But I just couldn't go through with it. I love life too much."

All Elif had done was simply decline the offer of an arranged marriage with an older man, telling her parents she wanted to continue her education. That act of disobedience was seen as bringing dishonour on her whole family – a crime punishable by death. "I managed to escape. When I was at school, a few girls I knew were killed by their families in the name of honour – one of them for simply receiving a text message from a boy," Elif said.

So-called "honour killings" in Turkey have reached record levels. According to government figures, there are more than 200 a year – half of all the murders committed in the country. Now, in a sinister twist, comes the emergence of "honour suicides". The growing phenomenon has been linked to reforms to Turkey's penal code in 2005. That introduced mandatory life sentences for honour killers, whereas in the past, killers could receive a reduced sentence claiming provocation. Soon after the law was passed, the numbers of female suicides started to rocket.

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Elif has spent the past eight months on the run, living in hiding and in fear. Her uncles and other relatives are looking to hunt her down, for dishonour is seen as a stain that can only be cleansed by death. One of the women's shelters where Elif has stayed has been raided by armed family members.

Elif is from Batman, a grey, bleak town in the south-east of Turkey nicknamed "Suicide City". Three quarters of all suicides here are committed by women – nearly everywhere else in the world, men are three times more likely to kill themselves. "I think most of these suicide cases are forced. There are just too many of them, it's too suspicious. But they're almost impossible to investigate," said Mustafa Peker, Batman's chief prosecutor.

Wearing tight clothes or talking to a man who is not a relative is sometimes all it takes to blacken the family name. Mr Peker said women who are told to kill themselves are usually given one of three options – a noose, a gun or rat poison. They are then locked in a room until the job is done.

A woman's fate is usually decided during a "family council", when the extended family meets to discuss breaches of honour. In these meetings, it is agreed how the victim must be killed. If it is not to be a forced suicide, a killer is chosen. The youngest member of the family is often ordered to kill, in the belief they will be treated more leniently if caught.

Mehmet was 17 when he was handed a gun and told he would have to kill his stepmother and her lover. "I didn't want to do it. I was so young and so scared," he said. Mehmet ran away, but his family tracked him down and warned him his own life would be in danger if he refused to kill.

He shot dead his stepmother's lover, but his stepmother survived the attack. He was given a two-and-a-half- year prison sentence.

"There were many other 'honour killers' in prison and we were treated with respect, even by the prison guards," Mehmet said.

Most honour killings happen in the Kurdish region, a barren land ravaged by years of war and oppression. Rural communities here are ruled under a strict feudal, patriarchal system. But as Kurds have fled the fighting between separatist rebels and Turkey's government, the crime is spreading across the country into its cities and towns. According to a recent government report, there is now one honour killing a week in Istanbul.

"Families who move here are suddenly faced with modern, secular Turkey," said Vildan Yirmibesoglu, the head of Istanbul's department of human rights. "This clash of cultures is making the situation worse as the pressure on women to behave conservatively is become more acute. And of course there are more temptations."

Ms Yirmibesoglu believes that the entrenched belief in the notion of honour – at all levels of society – is impeding any progress. "Honour killings aren't always properly investigated because some police and prosecutors share the same views as the honour killers," she said. "For things to change, police, prosecutors and even judges need to be educated on gender equality."

Killing for Honour will be shown on Channel 4 tonight at 7.35pm