Mir Hossein Mousavi makes an unlikely rebel leader. He is white-haired, soft-spoken and pale-faced. He was pulled out of retirement for one last campaign and looks like it. If he boarded a crowded London bus, he would probably be offered a seat.

What the Iranian authorities misjudged, however, when they rigged the vote in last month’s elections and returned President Mahmoud Ahmadinejad to power with an absurd landslide victory, was the character of the man they expected to accept defeat and bow out gracefully.

Yesterday Mr Mousavi counter-attacked by denouncing the crackdown on dissent and urging his supporters to continue their protests against the regime. Ayatollah Ali Khamenei and Mr Ahmadinejad may have the full might of the Iranian state at their disposal, but they will have to move carefully against their stubborn foe.

Mr Mousavi is no pro-Western liberal. He was a key figure in the Islamic revolution of 1979. He is best remembered for running the country’s economy successfully through the bleak years of the Iran-Iraq war.

Like many of his countrymen and women, he does not like being pushed around, bullied or having his intelligence insulted by people he regards as his intellectual inferiors. His wife is even less diplomatic. His support extends to millions of ordinary Iranians and among powerful figures in the political and clerical hierarchy, including two former presidents. This is now a fight to the finish. Iran faces a long and painful war of attrition, pitting the hardliners against Mr Mousavi’s green revolution. The regime will hope that the show of force will wear down the opposition, as it did ten years ago during student protests. Mr Mousavi hopes that June’s demonstrations were the opening salvo of a new revolution that will sweep the leadership from power just as the Shah was dethroned 30 years ago.

The outside world has few easy options. It cannot be seen to condone Mr Ahmadinejad’s stolen victory, but neither must it be seen to meddle in Iran’s internal affairs.

Iranians must decide for themselves who their leaders should be. After all, that was the whole point of the presidential elections in the first place.

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