Political history was made last night when Mahmoud Ahmadinejad, Iran’s President, was forced to abandon an election rally because the crowds who gathered to hear him were too vast.

As many as 50,000 fanatical supporters of the Islamic fundamentalist President had stood jam-packed for four hours in suffocating heat inside a vast prayer hall in Tehran.

Outside, an overflow crowd almost as great blocked all access to the venue. Officials said that Mr Ahmadinejad’s vehicles spent 90 minutes trying to force their way through, without success. There was talk of him holding the rally outside, but the idea was dropped when officials warned that people would be crushed to death.

As Mr Ahmadinejad’s disappointed followers flooded on to the streets, supporters of the President’s strongest rival, the reformist Mir Hossein Mousavi, mounted their own show of might. Tens of thousands of them, all dressed in green, formed a human chain running the length of Valiasr, the thoroughfare that runs 30km (18 miles) from the north to the south of the Iranian capital.

As darkness fell last night the city was in chaos, with all traffic paralysed and rival groups rampaging through the streets in support of two leaders with radically different visions for the future of their country.

It was a highly combustible situation and testimony to the extraordinary passions and excitement generated by Friday’s election in which Mr Mousavi, a former prime minister, is fighting to become the first challenger to defeat a sitting president in the 30-year history of the Islamic Republic. Iranians say that the only other presidential election that has caused such fervour was when Mohammed Khatami was swept into power on a tide of reformist fervour in 1997.

The chasm that has opened up in Iranian society after four years of Mr Ahmadinejad’s ultra-conservative, socially repressive presidency were starkly apparent yesterday.

The President’s rally matched any that Barack Obama held last year in both size and ardour. It was attended by the deeply devout, the working poor — Iranians still consumed by revolutionary fervour. The men were bearded and draped in red, white and green Iranian flags; the women dressed in all-encompassing black chadors with their headscarves drawn tight. The sexes were segregated.

The supporters regard Mr Ahmadinejad as Iran’s saviour, the man who has rescued his country after the decadence of the Khatami era and restored its prestige. “He brought the revolution back to its true course,” Mohammed Saberi, 25, a student, said.

“He’s stood up to our enemies. He’s stood up to the United States with all its strength,” said Hassan Khani, 47, paralysed by shrapnel in the Iran-Iraq War, who was in a wheelchair.

The surging, seething sea of humanity demonstrated its commitment through sheer endurance. All afternoon it filled the massive hall with deafening noise, chanting “Ahmadi is our love”, “Death to Israel”, “Down with the enemies of Islam” and “Mousavi is a liar”.

Hour after hour, the frenzied multitude sang religious songs, recited verses from the Koran and roared approval for a string of sports stars, film directors and other Iranian celebrities who endorsed the President.

Barriers were swept aside. War veterans in wheelchairs were lifted over the heads of the multitudes to stop them being crushed. Those who collapsed in the intense heat were likewise passed through the crowds.

The Mousavi supporters who filled Valiasr were the polar opposite — predominantly young, liberal, urban and middle-class, people who are compelled to obey Islamic strictures in public but enjoy western lifestyles in the privacy of their own homes.

Here there was no segregation. Women wore make-up, sunglasses, jeans beneath open chadors, and headscarves that left most of their hair exposed. The men had daubed themselves in green facepaint, ribbons and headbands. Some even held hands.

With just four days left before the election, the morality police have all but vanished from Tehran’s streets and young Iranians are using the rare opportunity to run amok. Well into the early hours, the streets are filled with honking cars awash with campaign posters, young men and women hanging from the windows, music blaring and hazard lights flashing. At every junction rival groups of supporters chanted and jeered at each other. The squares are festooned with election banners and posters.

The police scarcely try to keep control, and a series of televised debates in which the candidates have cast decorum aside, accusing each other of corruption, fraud and cronyism, have merely fuelled the sense of anarchy.

If the vote were in Tehran alone, Mr Mousavi would be likely to romp home, but Mr Ahmadinejad has assiduously courted Iran’s more rural areas and is running as a champion of ordinary people fighting a corrupt urban elite.The two other candidates, Mehdi Karoubi and Mohsen Rezaie, stand little chance, but will split the reformist and conservative votes respectively. There are also fears of vote-rigging.

Most independent observers predict that no candidate will achieve 50 per cent on Friday, pitching Mr Ahmadinejad and Mr Mousavi into a run-off a week later.

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