Can guerrillas become statesmen? This is the dilemma of every revolutionary movement. Gunmen rarely succeed as lawmakers; Yassir Arafat's ultimate failure was as much due to his love of plotting and conspiracy as it was about corruption, oppression and Israeli intransigence.

Few revolutionaries have come to power with as much riding on them as Hamas, the Islamist resistance movement that grew out of Palestinian frustration with the squalor and hopelessness of the Gaza slums. When the masked fighters decided to lay down their guns - temporarily - to contest the Palestinian elections last year, they raised huge hopes: here, at last, was a disciplined and determined group to throw out Arafat's cronies, clean out corruption and bring dignity and jobs to the 1.5 million Palestinians imprisoned in the fetid strip. They won. And since then, everything has gone downhill.

The remarkable documentary, Inside Hamas, is eyewitness evidence of how power has become a poisoned chalice. “Can they lay down their weapons and behave like a government?” an Arab newspaper editor asks. The cameras track the challenges from the first day. Israel's hostility was implacable: until Hamas recognised its right to exist, there would be no talks, and no let-up in pressure. Above all, there would be no money. The West backed Israel and cut off aid, virtually the only source of money for a bankrupt government to pay teachers, police and thousands of other workers. The result: fury.

“We are living through a wave of starvation,” one demonstrator shouts at men in blue combat fatigues, the “executive force” Hamas created to ensure a loyal police force. “Attacking the enemy is different from policing the streets,” a police captain admitted sheepishly. Hamas made its name by confronting the Israeli occupiers. Its fighters see no reason to stop now: skirmishes on Gaza's borders are a part of everyday life, as Israeli tanks and bulldozers clear the scrub where Hamas fighters launch rockets. But confronting a furious crowd in the streets of Gaza was not how the movement's leaders planned to advance their cause.

Gaza is now a deeply riven society. Teachers, doctors and civil servants hate the Israelis, but know that the blockade will never be lifted while Hamas remains intransigent. “You are the cause of our hunger! There's no help, no pay, no nothing. We just want our salaries,” a Palestinian shouts. The daily confrontations start over a trivial incident, but quickly escalate. The police arrive to clear the crowd and soon raise their clubs to beat down the demonstrators - even as the cameras are running.

Hamas was once widely admired for its efficiency in delivering social welfare and in supporting the families of militants killed in clashes. Can the movement hang on to Palestinian hearts and minds? Hamas still clings to its Islamist principles, seeing no divide between its religious and its political absolutes. Ismail Haniya, the Prime Minister who split with President Abbas, speaks with the steely determination of those who see no room for compromise.

Not all Palestinians agree. Gaza's articulate middle classes tell the camera of their worries. “Hamas has taken over all the mosques. They preach only politics there.” The mosques are now flashpoints, with demonstrations at Friday prayers and those who oppose creeping Islamicisation worshipping in the street outside in protest. The camera is there to catch the confrontation when the police arrive and try to force those praying in the street back inside the mosque. “I'll beat all of you,” one enraged policeman says. “You talk about Jews but you are much worse,” a distraught woman replies.

Hamas is caught in a dilemma. Its authority is based on overwhelming victory in a democratic election. Its problems are caused by the world's refusal to accept that election result. Is collective punishment Israel's only answer? Should the outside world not ask whether it is time to talk to Gaza? Alas, the film does not say: we see no Israelis and hear none of the international debate. To enforce its rule, break the strikes and cope with the blockade, Hamas has to resort more and more to strong-arm tactics - which, even to its supporters, look like the classic bullying of dictators. As Peter Capaldi, the film's narrator, concludes: “Hamas is turning its back on toleration and trying to rule Gaza with an iron fist.” But was there ever a realistic choice?

Inside Hamas, Sunday, C4, 7pm; Michael Binyon is a Times leader writer and foreign affairs specialist

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