Making forecasts about Iran is a foolish occupation. Few predicted the surge of support for Mir Hossein Mousavi before the June election, or the regime’s egregious rigging of the result, or the vast protests that followed.

Even fewer would have predicted that six weeks later it would be the opposition rebounding and the regime in disarray.

A Government that claims to be the champion of Islamic values has been hit by its own version of America’s Abu Ghraib scandal. It has been caught perpetrating some of the very horrors for which the Shah was overthrown.

President Ahmadinejad also enraged his fellow conservatives by defying Ayatollah Ali Khamenei, his patron and Supreme Leader, when he selected a relative as his deputy.

Foreign journalists are now banned from Iran, and it takes the skills of a Kremlinologist to decipher what is really happening in Qom and Tehran, but it no longer seems absurd to ask whether Mr Ahmadinejad will survive.

The security forces have failed to crush the opposition. Mr Mousavi is about to launch a broad political front to demand justice and democracy.

Mr Ahmadinejad has forfeited whatever support he had in parliament, has powerful enemies within the political establishment, and faces a severe economic downturn that could be compounded by yet harsher international sanctions next year if the deadlock over Iran’s nuclear programme persists.

He knows, however, that his fate and the Supreme Leader’s are now inextricably entwined. Mr Khamenei has supported Mr Ahmadinejad so robustly, and sacrificed so much authority to ensure and defend his re-election, that to jettison his wayward protégé now would almost certainly destroy both of them.

Times Recommends

• Should Knox’s trial even have reached the courtroom?
• 'Was it real?' The US bailout nightmare
• Iranian opposition plays the long game