Oil at nearly $100 a barrel cannot keep Mahmoud Ahmadinejad safe in the presidency of Iran for ever. Finally, it seems as if his breathtaking economic mismanagement, squandering an unprecedented bonanza, may prise him from office.

His critics have been predicting from his election in June 2005 that his wilful ignorance of economics would lead to his downfall. They have been wrong so far because of oil prices even higher than expected; a still-deep hunger among the very poor for Ahmadinejad's message; and his fortuitously successful handling of the nuclear dispute with the West.

The parliamentary elections in March will be the best test of his support — and of whether clerics and other leading figures now want to turf him out. No successor is likely to be as amenable as the West wants on the nuclear front but even if Iranians find that standoff a source of national pride they may now reckon that they can pick someone better.

When he became President, oil was $60 a barrel; recently, it has been almost two thirds as much again. Few presidents have been so lucky. But as Ali Ansari, an academic specialising in Iran, argues in a subtle report for the International Institute for Strategic Studies, that was a blessing for Iran, forcing its leaders to be innovative and financially cautious. “One of the reasons why the Islamic Republic had been able to weather political storms ... had been that the management of the economy had ... been conservative and cautious. Particular care was taken with predicting the price of oil.”

Ahmadinejad, with his peculiar and literal belief that he has divine backing, was not inhibited by this record of prudence. With a total oil revenue in the first two years of his presidency of $120 billion (£61billion) — more than Ayatollah Ali Akbar Hashemi Rafsanjani had in his eight years as President — the administration still found it necessary to deplete the emergency oil reserve fund set up by Ahmadinejad's presidential predecessor, Mohammed Khatami. According to the Iranian central bank he took $35.3 billion from the fund in his first year and $43 billion in his second year, as a new book, Ahmadinejad, by Kasra Naji, records.

Nor is it easy to work out what Ahmadinejad has spent it on, because he has channelled much of it through religious foundations and to contracts of his own nomination rather than leaving it under the control of ministers and elected parliamentarians. But the predictable result of the spending was inflation, rising from 12 to 19 per cent. Many were put out of work by his sudden decision to raise the minimum wage by nearly half. The climax of this spectacle was the petrol rationing announced so suddenly on June 27, 2007, that motorists could not complete their journeys. For the fourth-largest exporter of oil in the world, that is a humiliation. In the run-up to the March elections to the parliament, the Majlis, there have been signs of a rift between Ahmadinejad and Ayatollah Ali Khamenei, Iran's supreme religious leader. The President's critics, once silenced, are now allowed full voice. MPs say openly that the real jobless figure is near 20, not 10, per cent.

Ahmadinejad believes that he was put in the presidency by divine will; critics believe that he will be removed from it by economics. Their prophecy has not yet come true but there is good reason why it might.

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