As Arash Hejazi sat in an Oxford coffee bar, members of Iran’s Basij militia in Tehran were demanding his extradition outside the British Embassy.

The previous day the Iranian regime had sent an Oxford college a letter of protest over a scholarship given to honour Neda Soltan, the student killed during a huge demonstration against electoral fraud in Tehran in June. The letter also suggested that Dr Hejazi was responsible for her murder.

For Dr Hejazi, who had tried to save Ms Soltan’s life, that was the final straw. He decided that it was time to speak out. It was time to reveal how the regime has sought to vilify, punish and silence him ever since he told the world, immediately after Ms Soltan’s death, how she had been shot by a government henchman for peacefully protesting against President Ahmadinejad’s disputed re-election.

Dr Hejazi is now living in exile in Britain, jobless and fearful, while back in Tehran the regime blackens his name and hounds his friends, family and colleagues. “I told the truth. I just did what I had to do, but there were dire consequences,” he told The Times. In short, a quirk of fate — that he happened to be standing near Ms Soltan the moment that she was shot — has turned his entire life upside down and made him “another victim of tyranny”.

Dr Hejazi, 38, was doing a one-year postgraduate course in publishing at Oxford Brookes University at the time of the June 12 presidential election, and returned to Tehran on a business trip the following day. On June 20 he was caught up in a street protest when he heard a blast, looked around and saw blood gushing from the chest of the woman next to him.

She collapsed. Dr Hejazi, who had trained as a doctor before switching to publishing, tried in vain to save her life. Within hours a video clip of that scene had flashed around the world, transforming Ms Soltan into a symbol of the regime’s brutality and of the Iranian people’s battle for freedom.

So powerful were the pictures that Dr Hejazi, realising that the regime would try to suppress the truth, fled back to his wife and infant son in Britain. A few days later, in interviews with The Times and the BBC, he told how Ms Soltan was shot by a Basiji on a motorbike who was swiftly caught by other demonstrators.

Dr Hejazi’s troubles began almost immediately. His father, a university professor, was interrogated for hours and ordered to tell his son to shut up. Senior officials in the regime asserted that Ms Soltan had been killed by foreign intelligence agencies, and that Dr Hejazi was part of an international conspiracy to undermine the Islamic republic. He was denounced in the state-controlled media. Iran’s police chief declared him a wanted man.

Although Dr Hejazi received thousands of e-mails praising his courage in speaking out, supporters of the regime threatened to kill him, and called him a murderer, a spy and Ms Soltan’s pimp. Oxford police installed alarms and a hotline in his two-bedroom rented house on the edge of the city but he still does not feel entirely safe. He opens his door with caution, and asks that his wife’s name not be published. “I worry for my security,” he said.

In Tehran the regime is exacting revenge on Caravan Books, the publishing house that Dr Hejazi co-founded and which employs 22 people. It has used Iran’s censorship laws to ban the publisher’s books and forbidden banks from giving it loans, even after Dr Hejazi resigned as editorial director. “They are trying to close the company down,” he says. He believes that the regime is pursuing him not just because he has seriously embarrassed it — “a lot of the pressure is to discourage others from speaking out”.

Dr Hejazi’s course ended in September but returning to Iran is obviously now impossible. “I would be arrested at the airport,” he said. He would join hundreds of other political prisoners who have been beaten, raped and tortured in the past five months. “I can be considered an exile.” He has been searching for a publishing job in Britain, however menial, but in vain. His wife has lost her post as a finance manager in a large Iranian company, and they are living on money borrowed from friends. “I can’t see my family. I’ve lost my job and my career. I don’t know how to sustain myself,” he said, laughing at the regime’s charge that he was an agent of foreign intelligence services. If he were, he said, he would not be living as he was.

While the regime makes Dr Hejazi and his family suffer, it has does nothing to punish the Basiji who shot Ms Soltan and was quickly identified by the demonstrators who caught him.

Dr Hejazi does not regret what he did and insists that he would do exactly the same again. He believes that he helped to expose the true nature of an evil government. “Totalitarian regimes always want to cover up their violence and terror, but evidence always surfaces to show the world what is really happening,” he said. He is proud that he rose to the challenge. “In every person’s life there are moments of truth that determine the sort of person you are, that test your beliefs and values. For me Neda’s death and speaking out was that moment, and I think I’ve been true to myself.”

For the rest of his life, however, Dr Hejazi will be haunted by the memory of the young woman’s face, her struggle to ask the question “why”, as her life ebbed away on that pavement.

He still suffers flashbacks. “As a doctor I’ve seen death many times,” he said. “But Neda’s innocence, the injustice of her death, and her gaze before she passed away mean I can never heal.”