Most of us know the script off by heart now. The US threatens Baghdad. Politicians of the left, liberal journalists and members of the public protest. Retired generals warn and some European governments demur. Saddam Hussein makes a half-hearted gesture to western public opinion, which the US rejects. The US drops its bombs and we quickly forget about Iraq for another few years.
But today, things are very different. George Bush is no longer playing the game of containment. For sure, none of us can be certain what the US intends and it is possible that all the huffing and puffing is an elaborate propaganda battle both to convince US public opinion that the war on terrorism is succeeding, and to force Saddam to let the weapons inspectors in. But if these are games, they are games for very high stakes. President Bush has now raised the spectre of Saddam as the prime enemy, and the solution is no longer the identification and destruction of Saddam's weapons of mass destruction. Now regime change is the only way forward. How, without losing face and losing too many seats in the Senate and House of Representatives in the November elections, can he back down?
A regime change raises the stakes for Saddam. During the Gulf war, rumour had it that the threat of overwhelming retaliation kept Saddam's missiles and weapons of mass destruction firmly locked away. But a change of regime gives Saddam nothing to lose if he chooses to unleash whatever he now has on his neighbours. High-risk all round.
Around the world, Saddam is widely despised as a brutal dictator who has used chemical weapons - but everyone has a different approach to the way forward. Arab governments oppose conflict. The Spanish and Italian governments offer support to the US. The French and German governments insist on new United Nations endorsement before military action can take place. In Germany, Chancellor Schroder's Social Democrats will refuse to support any military action. Kofi Annan says military action would be "unwise", given the state of play in the Middle East.
Here at home, Lord Bramall, former chief of the defence staff, warns that we may become embroiled in a long-term conflict, while bishops warn that war would be immoral.
So which way should Britain and Tony Blair turn? Should we stick unconditionally with the US, maintaining the special relationship at all costs and perhaps privately urging caution?
However tempting that is, it would be disastrous - especially with parliament in recess. Many Labour and opposition MPs have been vocal for months, expressing their doubts about the US position and their concern lest Britain be drawn into a conflict not of its making, and not even in its interest. Before we commit our own servicemen and women and ask them to risk their lives, before we risk the lives of countless Iraqi civilians, we must have a lot more certainty than we have now.
The British people are entitled through parliament to an informed debate on the human cost of war. Iraq is not Afghanistan. Iraq may have suffered from years of economic decline, but it is no failed state. We have no reason to believe that the Iraqi armed forces and even the Iraqi people will see western intervention as anything other than an invasion to be fought and resisted.
Military experts warn that any military action may not be a quick intervention, but lead to a protracted conflict over a long period. A war in those circumstances could be bloody and brutal, with casualties high on all sides, especially among the Iraqi civilian population. Who has made out the moral case for that form of action?
And what of the legal case? There is a right of self-defence under international law and, by extension, even a right to pre-empt any imminent attack by weapons of mass destruction. I would be forced to support action against Iraq if it were for that purpose, and so would the United Nations.
Months ago, there was talk of a dossier damning Saddam and his regime, presumably giving precise details of his programme for the construction of weapons of mass destruction and his capacity to threaten the world. But it is clear that there is not enough hard evidence to condemn Iraq, or we would have acted by now. So we must call Saddam's bluff and demand that the weapons inspectors go back with the remit to do their job properly, and according to UN resolutions.
There is no legal basis for regime change. How could there be, when it gives carte blanche to superpowers everywhere to kick out whatever regimes they fall out with?
If we go to war and win, what are the spoils? Regime change sounds fine. Who will regret Saddam's demise? But the problem of rebuilding Iraq with a US puppet government could make the reconstruction of Afghanistan, not yet a success, look tame.
There would also be a tremendous reaction throughout the Middle East. The anger and frustration that US action engendered would be seized upon by radical groups whose own agenda may be every bit as bad as Saddam's. With an election looming in Turkey, and a succession battle for the Saudi throne, these questions deserve an answer.
We also need to know the cost of this war: not in money terms alone, but in the services that a Labour government will no longer be able to provide in our schools, our health service and other areas of public spending.
Wider afield, we need to debate the impact on the world economy if oil prices are destabilised. Oil experts are discussing scenarios from oil tumbling to $6 a barrel or rocketing to $60. It is impossible to believe we can easily ride such destabilising forces.
These are desperately serious issues, not intellectual parlour games, and we have got to have proper answers. If these are not forthcoming and Britain drifts into a war without national consensus and consent; if the mood is that this war is more about US domestic politics than preventing Iraq unleashing terror on the world, there will be an enormous outcry, certainly among back-bench Labour MPs in parliament, and much more widely among a public whose revenge takes place at the ballot box.
Tony Lloyd is a former minister of state at the Foreign Office (1997-99)