Ari Mahmod held his head up when he went to prison. He felt no embarrassment. And why should he? After all, he said, it was not as if he was locked up for something as inconsequential or shameful as theft. He was sure that, back in the real world of suburban Mitcham, south London, among his own people, they would be thanking his family for what he had done, taking pride in the decisive way he had acted.

Many people might find it hard to comprehend that any man could take pride – pleasure, even – in the brutal murder of his niece. Banaz Mahmod had been beaten, probably raped, and finally strangled with a bootlace in the living room at home. Her uncle Ari had not been there, but he had planned it, knew exactly what was happening, and had been waiting nearby…waiting for his family reputation to be restored.

As he liked to say, in his culture, reputation was more important than life itself. That was why it had to be done – why his brother’s daughter had to die.

In Kurdish Iraq – as elsewhere in parts of south Asia and the Middle East – they would not even have needed to bother hiding the body. Honour crimes – such as the recent stoning to death in Iraq of Du’a Khalil Aswad, a 17-year-old Kurdish girl who had fallen in love with the wrong boy – were at the time often committed by a group or crowd of men, quite openly, in public.

In Du’a’s case, her death had been recorded on mobile-phone cameras and uploaded onto YouTube, where two police officers could be seen standing about doing nothing while Du’a was killed. In Kurdistan, honour crimes are still being committed at the rate of three or four a week and, despite a recent tightening of the law, offenders are still going unpunished or receiving light sentences.

But in Mitcham, purifying the family shame was not quite as straightforward as Ari might have wished. And not everyone thought being an honour killer was quite so honourable.

Ari’s teenage daughter Ala had been in the house on the day in December 2005 when the men of the extended family gathered to agree between themselves that Banaz would have to die. While the men were talking, Ala overheard what was going on. She was upstairs at a computer having a discussion on MSN Messenger with her cousin Jwan.

It emerged that Ala had been told Banaz was having an affair. She thought that was disgusting, and said Banaz would go straight to hell, but “if I find out anyone will kill her I will go to the police”. Jwan warned her to be careful: “They’ll kill you next.” Ala said she was not going to sit and keep quiet about something like this, it was too serious. “This is someone’s life. Who gives a shit what some flippin’ immigrant butchers think. Who are these guys to talk? None of them are innocent.”

This too – the family council meeting, a kind of crisis-management team – was a cultural tradition the Mahmods had brought with them from their rural tribal homeland in the Sulaymaniyah district of Kurdistan, where their land and property titles and powerful ancestors had bestowed upon them the inherited title of agha – lord – which went with their name.

Ari Mahmod Babakir Agha was the head of the family, one of four brothers who were all now living with their wives and children in south London. He was not the eldest brother – that was Mahmod, the father of Banaz – but for a number of reasons, primarily based on Ari’s success as a businessman since coming to the UK in the 1990s, and Mahmod’s family troubles, Ari had taken the ascendant role. The two older brothers, both in their early fifties, had little time for each other, and Mahmod had suffered a degree of social exclusion from the wider family.

Ari was not the only one who thought Mahmod was weak. And perhaps Mahmod, like many others, thought Ari was arrogant, lording it over the rest of his family, especially at his home in Mitcham, which was much larger than Mahmod’s. He had a Lexus on the drive and inside a shag-pile carpet so deep you could get lost in it.

Ari would sit sprawled in the centre of the sofa with his arms outstretched, the lion king overseeing his domain. Everyone else would arrange themselves humbly around him.

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