A diminutive 64-year-old grandmother who refuses to be bound by the rigid constraints imposed on women in Iran proved more than a match for the President of the Islamic Republic yesterday.

Zahra Rahnavard had already broken all precedent by actively campaigning for her husband, Mir Hossein Mousavi, a relative moderate who is President Ahmadinejad’s strongest challenger in Friday’s presidential election. Yesterday she went a step further by summoning the domestic and international media to a press conference at which she tore into the President for lying, humiliating women, debasing his office and betraying the principles of the revolution.

What sparked her fury was Mr Ahmadinejad’s televised debate with her husband last week in which he challenged Dr Rahnavard’s considerable academic qualifications, suggesting that they were earned not on merit, but through the patronage of a corrupt political elite.

“He wanted to destroy his rival through lies,” she declared in a 90-minute finger-wagging tour de force, and she vowed to sue the President if he did not issue a public apology within 24 hours.

It was a more forceful attack than any of Mr Ahmadinejad’s three male challengers have managed, and would have been remarkable in any election, let alone in male-dominated Iran. It also injected more uncertainty into a race that already has an outcome impossible to call. Dr Rahnavard’s boldness is likely to enrage conservatives, but should delight the women and young urban Iranians who must vote in great numbers if Mr Mousavi is to unseat the incumbent.

Dr Rahnavard offered further inducements. She promised that her husband, if elected, would appoint women to Cabinet posts for the first time, and name many female deputy ministers and ambassadors. He would end discrimination and ensure that women were no longer treated as second-class citizens. He would release women’s rights activists from prison and abolish the “morality police” who, during Mr Ahmadinejad’s first term, cracked down on women deemed to be dressed inappropriately. She even suggested that women should not be forced to cover their heads.

Dr Rahnavard, a writer and sculptor whose works adorn some of Tehran’s squares, enjoys some protection from conservative attacks because of her own revolutionary credentials. In the last years of the Shah, she was close to Ali Shariati, a dissident Islamist philosopher, and fled to the United States after his arrest. She returned just before the revolution in 1979 and helped to develop the new republic’s cultural and political programmes.

She later served as a political adviser to Mohammad Khatami, the reformist President from 1997 to 2005, and as chancellor of al-Zahra university for women in Tehran — until she was removed by Mr Ahmadinejad’s Government in 2006 because she had invited Shirin Ebadi, the Iranian human rights activist and Nobel laureate, to give a lecture.

In recent days she has lent sparkle to the campaign of her distinctly low-key, uncharismatic husband, introducing him at rallies, addressing meetings solo and writing newspaper articles. She sends unmistakable signals to reformist voters by wearing a floral headscarf and open black chador that reveals colourful clothes beneath, and appearing hand-in-hand with her husband on the election posters that festoon Tehran.

She has even been likened to Michelle Obama — a comparison that she rejected in halting English yesterday. “I am not Michelle Obama. I am Zahra Rahnavard. I am a follower of the daughter of the Prophet Muhammad, who has the same name,” she said. Mr Ahmadinejad’s wife is never seen and few Iranians could even name her.

With his wife’s help, Mr Mousavi, a former prime minister, is gaining momentum, and his supporters — clad in green — are out in force on the streets of the capital. On Saturday he was about to address 15,000 people in Kharaj, a town west of Tehran, when the electricity was cut in what Dr Rahnavard suggested was an act of sabotage. “Were angels involved, or devils?” she asked pointedly.

Dr Rahnavard’s aides made sure that plenty of foreign journalists were present at yesterday’s press conference, lest the state-controlled media sought to ignore it.

Scarcely visible behind a bank of microphones, she accused Mr Ahmadinejad of humiliating not just her, but all Iranian women, and of seeking to block their progress and deny them higher education. She said that he had violated his constitutional duty to defend the rights of all Iranians, and brought shame on his office. “I will not relax until I teach him a lesson,” she declared.

Many liberal Iranians are reluctant to vote lest they legitimise the regime, but Dr Rahnavard implored them to turn out on Friday.

“My dear friends, if you don’t vote, this minority, this destructive team, will win again,” she said.

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