When one of my colleagues walked into a Lebanese village last year, a 12-year-old boy pointed a toy gun at her and said: "Britain is against us." Thousands of Lebanese people blamed the British government, not just Israel, for the bombs that had fallen on their homes, because the UK had failed to press Israel to stop its disproportionate response to Hizbullah's attacks on civilians.

What Britain does or does not do overseas has a profound effect on Oxfam's work. We see up close the human consequences of foreign-policy decisions made by our leaders.

For four years, foreign-policy debate has been dominated by the fallout of the decision to invade Iraq. And Oxfam's aid workers in the world's conflict zones have been hearing more and more frequently the kind of anti-British sentiments expressed by that boy in Lebanon. The danger is that, as a reaction to this, foreign policy could lurch towards the opposite extreme, to an overly cautious approach. That could have potentially serious consequences for the people we work with every day.

The decision to invade Iraq has had appalling consequences for many people in the Middle East. It is vital that the deadly legacy of that bad decision does not spread, impacting on our response to other conflicts in other countries, and stopping innocent people who are threatened by genocide, war crimes or serious human rights abuses from getting the protection they need from the international community.

So when politicians speak about a new approach to UK foreign policy, they must have a longer memory than Iraq. After Rwanda and Bosnia, a Labour government came to office determined that Britain would never again allow mass murder to continue, and arguably pursued a relatively successful foreign policy until the misadventure in Iraq. The current government has championed the idea that the UK, like the rest of the world, has a responsibility to protect civilians from genocide and war crimes. Two years ago, Tony Blair played a vital role in securing international agreement on this.

The trouble is that Iraq has undermined Britain's ability to deliver on that commitment and to be able to save lives in other conflicts. Last November, Sudan's president was, for example, able to deflect criticism and denounce the plans for a UN force to protect civilians in Darfur, a proposal strongly backed by Britain. The impact, he said, would "be the same as what is happening in Iraq".

Any future prime minister needs to set foreign policy on a new direction, based on sound principles. I would suggest five. First, the UK should be active in trying to protect civilians around the world. Second, it should challenge everyone who commits war crimes and rights abuses. Third, the government must focus on coherent strategies for delivery as much as good ideas. Fourth, foreign policy must adapt to a changing world. It should be willing to distance itself from ill-judged US policies, when necessary, and rebalance its relationship between the US and the EU. We are moving to a multipolar world, in which China, India and others will be vital global players. Britain must find a better way to work with the world's emerging major powers, not least to influence them towards higher standards of human rights. Finally, the UK must be active with others, strengthening the UN and other multilateral organisations.

This government has been right to pursue an active foreign policy after the grim failures to halt genocide in the mid-90s, and to show wider leadership - from development to the arms trade. Future prime ministers should draw lessons from more than just Iraq as a new direction in foreign policy is set.

Barbara Stocking is director of Oxfam. bstocking@oxfam.org.uk

© 2007 The Guardian