Iran's President Mahmoud Ahmadinejad is moaning that missile strikes haven't hit Israel hard enough. The Americans say they support Israel's military attack on Iran the previous day, but won't actively engage in this war. And the Israelis are counting their country's civilian deaths and wondering if they should launch a second strike on Iranian nuclear facilities, to "finish the job".

This is all part of a war simulation game staged by an Israeli thinktank last month, to which a British film crew were given sole access. The result is a game-time enactment of what would happen if Israel does attack Iran.

For some time, Israeli prime minister Binyamin Netanyahu has been escalating talk of a military strike, to prevent Iran from building its first nuclear weapon. The prospect of war, and recent disaster drills to prepare for it, have terrified his own people, and the rest of the world. Israeli military and intelligence chiefs say a strike is a bad idea, while the Obama administration has told Israel to back off and wait for sanctions to work.

If Israel hit Iran's nuclear facilities, would Hezbollah, Iran's allies in Lebanon, join in to retaliate? Would America step in to help its best friend in the Middle East? This filmed simulation shows a group of Israeli ex-spooks, former politicians and military officials split into teams to role-play the consequences. I have not seen the full film, but was in the cutting room for a couple of days helping with translation and the scenes I saw were compelling. Team Israel, taking stock of Iranian missile attacks on civilian targets, makes the operational assumption that the situation won't spiral totally out of control.

Is that a reasonable prediction, or totally delusional? The documentary has an interview with an Iranian former nuclear negotiator and foreign policy adviser, who returns the simulated salvo by saying that Israel has grossly underestimated Iran's capacity for retaliation. Iran, he says, would assume American complicity in any Israeli attack and take aim at US targets in the Middle East. When the US staged their own simulation of this same situation, in March, it predicted that an Israeli strike would lead to a wider regional war.

Now, the UK is thinking about putting warplanes in the Persian Gulf as tensions rise. And American military commanders have warned Israel that an attack on Iran could stunt US action, by cutting off key logistics support from Gulf countries that host US bases.

Watching scenes from Nuclear War Games, the bit that struck me most was a clip in which the Israeli role-players, having achieved their attack goals, are talking about a UN resolution – wondering if they should launch a final strike before ceasefire, and whether the US can be persuaded to make the resolution state "regret" rather than "condemnation" over Israel's actions. Listening in, you can't help feeling that this conversation has played out before – in real wars; in real life.

Dispatches: Nuclear War Games is on Channel 4 on Monday 5 November at 8pm