As darkness falls the floodlit domes and minarets of the great Jamkaran mosque begin to glow in translucent greens and turquoise. Coaches, cars and minibuses soon clog the four-lane highway leading up to the vast complex in the desert outside the holy Iranian city of Qom. By 10pm perhaps 200,000 pilgrims have poured into the concourse in front of the mosque – as they do every Tuesday night – for two hours of prayer and preaching.

The pilgrims are young and old, men and women, the latter dressed in all-encompassing ink-black chadors. Many have brought babies and children, rugs and picnics. They have come from across Iran to pray for the reappearance of the Mahdi, the Hidden Imam, the 12th successor to the Prophet, who – Shia Muslims believe – was born in AD868, vanished as a young boy, but will return to save humanity when the world is engulfed in violence, corruption and injustice.

These are busy days for the mosque, built where the Madhi was allegedly seen one Tuesday night in AD984. Pilgrims are arriving in ever-greater numbers, its facilities are being rapidly expanded and its most celebrated visitor is President Ahmadinejad, who has suggested that his Government’s mission is to prepare Iran for the Mahdi’s return.

The pilgrims see signs that that moment may be nearing – wars in Iraq and Afghanistan, greed, social injustice and moral decay. They are shocked by the decadence of cities such as Tehran – the make-up, the figure-hugging clothes, the skimpy headscarves. They laud Mr Ahmadinejad’s attempt to reimpose the strict Islamic mores relaxed by President Khatami’s reformist Government between 1997 and 2005. “He’s bringing morality back. He’s defending our religion,” said Muhammad Kazeim, 24, a nurse.

These pilgrims are decent, devout people whose traditional, conservative views are probably shared by the majority of Iranians. However, those views often conflict with Western ideas of freedom, and many urban Iranians now accuse Mr Ahmadinejad’s Government of imposing suffocating restrictions, censorship and repression inspired as much by politics as religion.

The most obvious manifestation of this changed atmosphere are the “moral police” whose “guidance patrols” are an almost permanent presence in Tehran’s congested squares – not just in the summer, when people naturally wear less. They stop women for bad hijab (headscarves), high boots, tight jeans or bright clothes, men for ostentatious Western hairstyles, men and women for holding hands.

But the backlash against Western culture goes much farther. Sometimes it is trivial – a Tehran restaurant chain called Apache, for example, was ordered to adopt a more Islamic name. Sometimes it is more serious, as in the case of the Museum of Contemporary Art.

Locked away in the museum’s basement is one of the world’s finest collections of modern Western art – works by Renoir, Picasso, Monet, Van Gogh, Jackson Pollock, DalÍ, Magritte, Gauguin, Toulouse-Lautrec and others collected by the former Empress of Iran, Farah Pahlavi, before the Islamic Revolution and now worth more than $3 billion (£1.5 billion).

They were last displayed just after Mr Ahmadinejad’s Government took office in 2005. The long-planned exhibition was so popular that the Ministry of Culture could not shut it down immediately and demanded the removal only of a Francis Bacon triptych with homosexual overtones. But Ali Reza Samiazar, who resigned as the museum’s director when he saw the tenor of the new Government, believes that it is very unlikely the collection will be shown again because the Government would see that as “promoting Western values and culture”. Instead, he says, the museum now stages exhibitions with ideological themes about the Islamic revolution or Islamic resistance.

Habibollah Sadeghi, Mr Samiazar’s successor, cancelled a meeting with The Times this week, but has in the past described Western art as an “aggressive, dominant” force to be resisted. Nor is it just Western art that is now being censored. The output of Iran’s world-renowned film industry has plummeted because its directors are reluctant to invest in films lest they are banned.

Dariush Mehrjui, one of Iran’s most famous directors, told The Times how the Ministry of Culture blocked his latest film, Santoori – about a musician who becomes a heroin addict – three days before its much-heralded release.

“It’s like your ship suddenly sinking, and this is all because of their censorship policy,” he said. “In the past 25 years it’s never been so bad . . . These are very hardline people who think dogmatically . . . The difference between Ahmadinejad’s Government and Khatami’s is 180 degrees.

“This Government thinks whatever was done under Khatami is antirevolutionary.”

Reformist newspapers have been shut. The rest do what they are told. Not one has dared to print a story much talked about in the capital this week about a top official in Tehran who was forced to resign after being caught with prostitutes. Two dissident websites recently published a leaked government directive to the media on how to cover political events.

UN Security Council condemnation of Iran’s nuclear programme should be presented as an “interference in Iran’s domestic affairs”, it said. Reports should say that “Iran’s peaceful nuclear programme will serve the Islamic world”, and that “the West does not want Muslim scientists to have access to modern technology for their energy industry”. They should highlight policy differences between Europe, the US, Russia and China.

Few foreign journalists are still permitted to work full-time in Iran. The Times was allowed in for ten days to cover the elections. We had to register with the Ministry of Culture and Islamic Guidance, employ an official translator and obtain written permission to visit anywhere outside Tehran.

This week the Government announced that it was investigating Noureddine Pir Mouazen, a reformist MP, for treason. He gave an interview critical of yesterday’s elections to Voice of America, a US-funded station that the Government regards as a vehicle for propaganda against the Islamic republic. “There’s an enormous paranoia about foreigners that pervades everything,” a Tehran-based diplomat said. That paranoia also extends to organised dissent, especially by women’s rights organisations.

The pilgrims of Jamkaran can rest assured that Mr Ahmadinejad is rolling back the liberalisation of the reformist era. Whether the Islamic republic he is rebuilding is one in which they want to live is another matter.

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