If ever the European Union were needed to promote human rights around the world, now is the time. The Bush administration's use of torture and detention without trial has decimated its credibility. With China professing at best indifference to governments' domestic rights practices and Russia coddling tyrants, the leadership mantle is there to be seized.

Yet the sad truth is that the EU is punching well below its weight. As a collection of democracies founded on respect for the rule of law and the rights of the individual, the EU should be a natural human rights leader. It has performed impressively in extending these values to its new members and occasionally elsewhere, but when acting beyond its borders, the EU is often disappointingly weak.

Much of the problem lies in the difficulty of achieving a common position among 27 members who hold the right to veto a proposed policy. Whatever sense that makes for internal policies on, say, tax or trade, it is a disaster for projecting EU influence abroad. It takes only one government with deeply felt parochial interests to block an effective EU position.

EU policy on Uzbekistan illustrates the problem. After the Uzbek government massacred hundreds of demonstrators in the city of Andijan in May 2005, the EU imposed sanctions. Today, many EU members favour continuing those sanctions until Uzbekistan permits an independent investigation or undertakes significant structural reforms. Germany, however, would settle for an empty human rights "dialogue" and is threatening to impose that tokenism on the rest of the Union.

This tilt towards the lowest common denominator reflects a preference for unanimity over effectiveness. Because the EU never acts beyond the wishes of its most reluctant member, it ends up doing little or nothing in places such as China, Russia, Darfur or even the US. There must be a better way.

One option would be to allow a supermajority, rather than unanimity, to achieve a common foreign policy - one of the aims of the apparently stillborn constitution. But that would require EU governments to give up their prized veto - a step that some are unwilling to take in spite of the unanswered pleas for help from repressed people worldwide.

Even accepting the unanimity rule, improvements are possible. The EU demands consensus at an absurdly petty level. At the United Nations Human Rights Council, for example, rather than approve a broad strategy and trust their representatives to pursue it wisely, EU members insist on signing off on each proposed resolution, word by word. This micromanagement makes the quick diplomatic give-and-take needed to build majorities impossible, partly explaining why abusive governments are running circles around the Union.

The EU could also treat its common position as a floor rather than a ceiling. It is appropriate to insist that no government do less than the common position on human rights issues, but why should no government do more? Too often EU governments use the lack of a strong common position to justify the lack of a strong national one. When human lives are at stake, that prioritisation of the collective over the effective is callous.

Even when a common position is reached, the EU's insistence on working almost exclusively through its "presidency" often undermines its clout. It is difficult to imagine a less effective way to maintain continuity or build expertise than the EU's rotating blur of six-month leaders, even when bolstered by the incoming president and other EU officials to form a leadership troika. The refusal to assign long-term responsibility on certain issues to the governments best placed to address them is a recipe for dysfunction.

In some cases, such as negotiations with Iran over its nuclear programme, the EU has appointed a permanent leadership team, but not for human rights. The Union's clout would be greatly enhanced if, rather than dispatching a team of fresh faces every six months, the same governments kept showing up at a trouble spot year after year, representing a continuity of concern and a determination to follow through.

These procedural failings cannot fully explain the EU's leadership failure. Part of the problem is a simple lack of political will. Promoting human rights can be costly and difficult, so many governments settle for lip service. But with US leadership in short supply, the people of the world are paying the price for the EU's weak performance. It is time to do better.

The writer is executive director of Human Rights Watch