No one seriously doubted that Mahmoud Ahmadinejad and his hardline supporters in the Iranian regime had the muscle needed to hold on to power — with or without a fresh mandate from the country’s voters.

But keeping it for the next four years in the face of a powerful opposition movement could be much harder.

Iran may be entering one of its most dangerous and unstable periods since the revolution 30 years ago, with reformists and hardliners within the regime in open conflict.

Since he came to power in 2005, the Iranian President has strengthened key alliances in the Islamic Republic and consolidated his control over the State. With the tacit backing of the Supreme Leader, Ayatollah Ali Khamenei, Mr Ahmadinejad increased the power of the Revolutionary Guards — the shock troops of the revolution — and the Basij, a paramilitary force with members in every corner of the country.

He has also moved to purge suspected reformists from key government posts, such as ambassadors serving in the Iranian foreign ministry and senior lecturers at university. Journalists and human rights activists critical of his rule have been intimidated or locked up, opposition newspapers closed and opponents forced to leave the country. It was no coincidence that the Interior Ministry was the same government body responsible for counting the votes, announcing the results and flooding Tehran’s streets with riot police to put down the ensuing protests.

But as the demonstrations over the weekend showed, Iran is not a stalinist dictatorship. Trying to rule exclusively by force is not feasible over an extended period.

For a start, Iran is now part of the global community. People have mobile phones, access to the internet and satellite television. The state monopoly over the media has been broken and young Iranians are better informed than ever before about what happens in their country and better able to communicate with one another.

Then there is Iran’s unique constitution, which was deliberately created to avoid the rise of a new shah.

At the top is the Supreme Leader, with almost limitless powers. Beneath him are competing branches of State — the presidency, parliament, the judiciary, the Guardian Council and the security forces. Ayatollah Khamenei may, on paper, have supreme authority but in practice he rules by building a consensus among the various strands of government.

Mr Ahmadinejad has the support of many important and powerful bodies in Iran but, as the election campaign revealed, he has also made many enemies and is deeply unpopular with the young, urban population — the fastest growing group in the country.

By far the biggest threat to him comes from Hojatoleslam Ali Akbar Hashemi Rafsanjani, the former president and one of the richest and most powerful politicians in Iran, who is head of the Expediency Council.

He is suspected of supporting the main opposition campaign against Mr Ahmadinejad by Mir-Hossein Mousavi. During one of the television debates, Mr Ahmadinejad even attacked Mr Rafsanjani and his sons for corruption.

Mr Rafsanjani may not be the dominant figure he once was in the early years of the revolution but he still wields enormous influence in parliament, with the clerics in the holy city of Qom and with the bazaaris, the powerful merchant class.

Keeping a lid on this dissent will be a huge challenge for Mr Ahmadinejad, not to mention the looming showdown with the West over Iran’s nuclear programme, which will come to a head by the end of the year.

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