Clare Short: Acting as Mr Bush's figleaf has been a tragedy for Britain

For the past few weeks, the spin has been that Tony Blair has been battling with Gordon Brown to ensure that we keep open the possibility of a referendum on the euro in this Parliament. This has rather sullied the Government's promise that the decision would be made in Britain's economic interest. It now seems that Tony Blair considers membership of the euro crucial to enable Britain to play a leading role in Europe as part of Britain's destiny.

All of this sits a little oddly with Tony Blair's previous escapade which was to side with the United States and cause a bitter conflict with France and Germany, in order for President Bush to rush to war in Iraq. He went on to pour scorn on President Chirac's vision of a multi-polar world and insisted that Europe must have a supportive relationship with the US.

It is perhaps worth pausing to ask how the conflict in Iraq has affected Britain's relationship with the US and Europe, and to consider what role the UK should seek to play in a world that is now dominated by one hyper-power.

As Donald Rumsfeld made clear before the Iraq conflict began, the US did not need the UK in order to fight in Iraq. It had more than enough military capacity to overwhelm a sanctions-weakened Iraqi army. The UK's usefulness was essentially political.

Without the UK, America would have been acting alone. This would have made it much more difficult for the Bush administration to persuade the American public to support a war. It is notable how much stress was placed by the US on the fact that it was acting in a coalition in Iraq. In practice, there were at least 255,000 US troops, 45,000 from the UK and a few Australian planes. Most of the rest of the "coalition" of 40 or so nations were weak and vulnerable countries, willing to add their name to the list rather than risk alienating the US.

One of my deep disappointments is that Tony Blair failed to use the leverage this gave the UK to help shape US policy on Iraq. It is now clear that the neo-conservatives - the hawks in the US administration - were determined to go to war and get rid of the Saddam Hussein regime from 1997 onwards. Donald Rumsfeld proposed action against Iraq immediately after 11 September 2001 - even though it was absolutely clear that there were no links between Saddam Hussein and al-Qa'ida.

From the summer of 2002, when the US started to hype up its rhetoric on Iraq, Tony Blair began to echo its stance. I and many others worked on the assumption that our Prime Minister was trying to repeat the role he played in the run-up to the Afghan conflict - to stay close to the US, try to prevent it lashing out and to try to build an international coalition to find a wise, internationally agreed strategy for dealing with Iraq.

It is increasingly clear that this was not the role that our Prime Minister played. Instead, he committed us, in the summer of 2002, to support the US if it decided to take military action in Iraq. Thus he lost all leverage. He could, and should, have said: we will join you if you agree first to the implementation of the roadmap to Palestinian statehood so that the people of the Middle East believe that we have a commitment to justice. Then we must act through the United Nations to get weapons inspectors back into Iraq, indict Saddam Hussein and lift sanctions so that Iraq can be brought into compliance with UN resolutions, the people's suffering brought to an end and Saddam Hussein's days numbered. We should have agreed that we had to be willing to threaten the use of force to move forward on Iraq, but we must exhaust all other means before launching any conflict.

Instead, the UK became the fig-leaf that enabled the US to pretend that it was not completely isolated in its approach to Iraq. Then the US and UK, with Spain trailing along behind, tabled a resolution on 16 March, saying that the requirements of Security Council Resolution 1441 had not been met. This meant that the UN's chief weapons inspector, Hans Blix - who achieved the dismantling of more than 60 ballistic missiles - was not allowed to complete the inspection process. But the US and UK found they had almost no support in the Security Council, and could not muster even a simple majority.

Tony Blair made a desperate last-minute effort to fulfil his promise by trying to persuade the Chilean President to table a compromise resolution listing the six steps Saddam Hussein had to take to comply with 1441, and by asking the US for a few more days. France made it clear it would not support this. The French view was that Blix must be given enough time, but that if this failed, the Security Council would have to authorise military action. Blair escaped from his dilemma by claiming that France had said it would veto any second resolution. It is now clear that was untrue, but the continuing vilification of France was the smokescreen behind which the failure to achieve a second resolution was hidden.

Since then, the Security Council has come together to pass a resolution lifting sanctions on Iraq and authorising the occupying powers to work alongside the UN on reconstruction. This resolution gives the UN a much smaller role in bringing into being a new Iraqi government than is normal. It was an unhappy compromise, but for the sake of Iraq and the UN the resolution was accepted.

Where now does this leave US-UK relations? Clearly, Tony Blair is much-fêted in the US and likely to get his Congressional medal. But dismissive statements about the likelihood of finding weapons of mass destruction from Rumsfeld suggest that the UK was more a convenience in time of need than an influential ally. The US remains unwilling to support Kyoto, the International Criminal Court or even the Convention on the Rights of the Child, and has recently threatened to install an execution unit at Guantanamo Bay, despite UK protestations.

As for Europe, there are strong rumours of a reinvigorated Franco-German alliance. It would be a tragedy if this leads to a refusal to reform the Common Agricultural Policy, and this means Europe blocking the Doha Development Agenda and a failure to deliver fairer trade rules for developing countries.

Europe is at a crossroads. Enlargement will challenge all its institutional arrangements and its sense of its role in the world. There are some who support a stronger, more united Europe because they are critical of the US and wish to build a federation with equal strength to counterbalance American power. This road can lead to a United States of Europe and a demand for increased military spending in an attempt to match the power of the US. Others of us believe that the European Union can act as a counterweight by standing up for different values.

I want a European Union with a stronger commitment to the UN and to multilateralism. The EU should also reform its development efforts and become a force for good by making a better contribution to development and justice for the poor of the world. We also need a real commitment to subsidiarity and a slimming-down of the bureaucratic regulation and inefficiency of the Brussels system.

These are some of the issues with which the Convention on the Future of Europe is meant to be grappling. Sadly, the UK influence is likely to be marginalised, partly because we took the wrong position on Iraq and made unjust attacks on France and Germany. On top of this, the debate in the UK is still so limited and polarised. This is a tragedy because a more coherent Europe could help the US to carry its power more wisely and help us build a more just and less polarised world.

Clare Short is participating in 'What The World Thinks of America', a global debate on BBC2 on Tuesday at 9pm