Across the city nervous Sunnis are learning to dissemble to avoid the killers, who are often dressed in police uniforms and set up checkpoints to examine people’s identity cards for obviously Sunni names. Many Sunnis have invested in forged ID cards. There is a website dedicated to teaching them how to fake it.

“At first we were joking about it but when our lives started to be threatened, the joke was over,” Assem, a 43-year-old shopkeeper, said. “It became a serious issue.”

Assem and his brother are former air force pilots, a group frequently targeted by Iranian-linked Shia groups seeking revenge for the damage done by Iraqi bombers in the Iran-Iraq War almost two decades ago.

Sausan began the lessons three months ago after hearing of a raid in Mansour, close to their home in west Baghdad. “Gunmen in Iraqi security forces uniforms stormed a company and asked the two guards to name all 12 imams. One of them failed and he was shot dead,” she said.

The teaching is not straightforward, and the doctrinal differences are often profound. Sunnis and Shias split soon after the death of the Prophet Muhammad, Sunnis believing that the Prophet’s companions should lead the community, Shia’s favouring a bloodline through his son-in-law Ali and grandson Hussein.

One day when Sausan was instructing Assem on the 12 imams, Assem’s brother and business partner walked in. “He was laughing and boasted that he already knew the names of five of the imams,” Sausan said. “I was surprised and asked him to name them — all five were the nicknames of the same imam. I laughed for a while, then told him to join the class.”

Assem has taken down the pictures of himself in his pilot’s uniforms and put up tapestry hangings of imams Ali and Hussein in his living room. In general, Sunnis frown at the display of human images as idolatry, but Assem, a middle-class Iraqi, has no strong feelings on the issue. “I feel very grateful to my wife and am lucky to have her,” Assem said. “I have lots of Sunni friends trying to do the same thing but they need someone they can really trust to teach them these things.”

A Sunni website has been set up to guide members of the once-dominant minority. It offers advice such as carrying a turba, a round prayer tablet made from clay gathered in the holy cities, or having Shia religious songs as ring tones.

The site also reassures devout Sunnis that it is not blasphemous to pretend to be a Shia. “According to the clerics, both Sunni and Shia, a Muslim can lie or even say words of sin if he is threatened to be killed.”

Many names in Iraq could be either Sunni or Shia, but for Marwan, 34, a car parts salesman, his clearly Sunni name could get him killed. He decided to buy a fake identity card, and contacted a Shia friend who had a relative working as a forger in Sadr City, bastion of the most dangerous Shia militia, al-Mahdi Army, named after the last of the 12 imams.

His uncle had already bought bogus cards for his family, which reaped dividends when Shia police commandos raided their house. They had been tipped off that the family were Sunnis, but were mollified when they saw identity cards from the Shia city of al-Hillah, south of Baghdad.

“The problem now is that I can’t drive my car, because the registration papers have my Sunni name,” said Marwan.

STAYING ALIVE

Tips on being Shia from the Sunni website Iraqi League

1 Practise imitating another personality and have an ID with another name (you can get these forged IDs from Muraidy market in Sadr city), especially if your name was Omar or Othman and if your family name was Dulaimy or Janabi, or if your birthplace was in one if the Sunni-majority cities

2 Memorise the names of the 12 imams

3 Learn to pray in the Shia way and carry turba [Shia holy clay] in your pocket.

4 Keep a turba in your house where it can be seen, and put up if necessary a black or a green banner on the roof

5 Keep a poster in your house of Imam Hussein. You can buy them in Mutanabi Street in Baghdad

6 Keep a copy of the Sajadi newspaper [a Shia paper that has Shia prayers] and read some of the prayers, some of them are touchingly beautiful

7 Keep a latmiya [Shia song] on your mobile phone

8 Learn how to curse Yazid and Maawia and Bani Omaya [early Sunni caliphs hated by the Shias] and in the way the Shias do

9 Wear or keep black clothes in your house, especially in ceremonies that demand it

10 Learn about the different Shia ceremonies (the death of the imams, their birth and the joy of Zahraa)

11 Pray in a husseiniya or a Shia mosque. Remember that Shia and Sunnis are not enemies, but there are misled, ignorant people and victims of evil plans who want to spread the breath of hostility in Iraq

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