By Edward Stourton
Analysis, BBC Radio 4
Grand Ayatollah Montazeri is one of Mahmoud Ahmadinejad's fiercest critics
It is not often you find an email from a Grand Ayatollah in your inbox - especially not when the Ayatollah in question is a pivotal figure in one of the great dramas currently unfolding on the world stage.
Grand Ayatollah Hoseyn Ali Montazeri is one of Shia Islam's most respected theologians - he was a moving spirit behind the revolution which gave birth to an Islamic state in Iran 30 years ago, and at one stage he was designated to succeed Ayatollah Khomeini in the role of Iran's Supreme Leader.
The month after this summer's disputed presidential election he issued a fatwa condemning President Mahmoud Ahmadinejad's government.
The Grand Ayatollah lives in Qom and does not often give interviews, but we thought we would take a punt by submitting some questions via his website.
The answers that came fizzing back make very strong copy indeed.
Montazeri tells Iran's clerics that they "can and must" act to bring about reform. They should, he declares, "be in step with the people" and tell them about their rights. He warns of dire consequences for Iran's religious authorities if they fail; the clerics' popular standing will, he says "become weaker and shakier".
It is to all intents and purposes an exhortation to take on the government.
The Grand Ayatollah's comments reflect a hugely significant shift in the dynamic driving events in post-election Iran. Mr Ahmadinejad does seem to have succeeded in suppressing the demonstrations which filled the streets of Tehran in the immediate aftermath of the vote.
But the popular anger that fired them has not gone away, and some of the most serious opposition to the regime now comes from the most unexpected source; many of the country's mainstream clergy and theologians want him to go.
Thousands of people protested against the result of the June poll
Because state and religion are presented as one and the same in the Islamic Republic, the sins of the state are tarnishing religion's reputation.
The problem has been growing for a while now; opposition journalists say all sorts of social ills, from drug addiction and prostitution to unemployment, are blamed on religion.
But with the election it has acquired a new dimension. Professor Ali Ansari of the Institute of Iranian Studies at St Andrew's University says that people were especially badly shaken by the fact that the violent post-election crackdown was carried out "in the name of Islam".
He cites the case of a minister's daughter who stopped praying because she was so shocked by what she had seen.
To many clergy it looks as if the actions taken by the president of the Islamic Republic are undermining support for the very religion the Republic was meant to serve.
And the clergy have another, more personal reason to fear the President; Mahmoud Ahmadinejad belongs to a minority sect of Shia Islam with a pronounced strain of anti-clericalism.
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is on BBC Radio 4 on Monday 19 October at 2030 BST, and Sunday 25 October at 2130 BST
One of the mainstream teachings of Shia Islam is that the Prophet Mohammed's authority was inherited by a line of spiritual leaders known as Imams, and that in the 10th century the last of them, the 12th Imam, went into what's known as occultation - that is to say he didn't die, but he has been hidden from humanity ever since.
One day, the teaching goes, he will return, ushering in an age of justice and peace and, shortly thereafter, the end of times.
It is very like the Christian doctrine of the Second Coming, and most Shia Muslims understand it in a similar way - as something that will happen in God's good time.
But Mr Ahmadinejad belongs to a minority sect called the Hasteners; they believe that it is the duty of the faithful to prepare the way for the return of the Hidden Imam - or Mahdi - and perhaps even to create propitious conditions.
Professor Ansari says this has led to some eccentric behaviour by the president's entourage.
They have meals where they leave a place at the table in case the Imam appears, they have spent large amounts of money refurbishing a well at a shrine where it is thought the Imam may appear, and, Professor Ansari says, "they've even had fanciful notions of, when they write their cabinet proposals, taking a note and dropped it down the well so the imam can be aware of it".
Many Iranians find this kind of behaviour eccentric, and most orthodox clerics regard it as something akin to heresy. But beyond that it is accompanied by some inflammatory anti-clerical language.
Mehdi Khalaji, a Shia theologian now teaching in the United States, quotes a warning from one of the president's close aides; when the Hidden Imam returns, he said, "the first thing he does is to behead the clerics because... they've been corrupted by money and politics".
Whether clerical discontent with Mr Ahmadinejad will harden into real and effective political opposition is still very much an open question, but it does seem very likely that religion will play a central role in what now happens in Iran - just as it did during the country's last great political upheaval thirty years ago.
Analysis: Ayatollogy is on BBC Radio 4 on Monday 19 October at 2030 BST, and Sunday 25 October at 2130 BST. You can also hear it later on the
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