Leading article: Giving the poor and weak a global voice

With the new year comes regime change on New York's East River. At midnight Kofi Annan stepped down as United Nations Secretary General. From today Ban Ki-moon of South Korea takes over; the first Asian in three decades to head the organisation.

There are no shortages of challenges in Mr Ban's in-tray. He must shake off the air of moral laxness that hangs over the organisation. The UN's reputation has been tarnished in recent years by the revelations of corruption in its handling of the Iraq oil-for-food programme and the sexual abuse scandal involving UN peacekeepers in Africa. Mr Ban's first task is therefore to reform the UN itself. His predecessor made only modest progress on streamlining the organisation's bureaucracy. The General Assembly rejected many of the changes first proposed by Mr Annan. The new Secretary-General is likely to face a difficult battle to push them through.

And then there are the grand geopolitical challenges of our times. From Sri Lanka to Darfur, regional conflicts are growing in intensity. Iraq is imploding. Sanctions have been imposed on Iran. North Korea conducted a nuclear test last year. The threat of international terrorism has grown. The slow killers of the modern world are still at large, too. Aids continues to ravage southern Africa and is a growing menace in Asia and Russia. Huge numbers of people still live in lethal poverty.

Mr Ban claims to be a pragmatist. In his election campaign he argued that the UN's strategic focus should be on "achieving the goals already set rather than identifying new frontiers to conquer". But to lead is to choose. What priorities will Mr Ban have now he is in office? We can perhaps surmise a little from his past. As a former South Korean foreign minister he has extensive experience of negotiating with North Korea. Helping to resolve the crisis on the Korean peninsula should be one of his priorities. Mr Ban also won support from China when running for the job, suggesting an ability to work with the emerging global superpower of the East. But will the new Secretary General be able to act as "the world's conscience" as Mr Annan did? Will he be able to work with the Bush administration in its final years? We shall have to wait and see. For now Mr Ban is an unknown quantity.

But we should not exaggerate the extent to which Mr Ban ought to make a difference. The unfortunate truth is the future of the UN is not in Mr Ban's hands. It lies instead in the hands of the five veto-holding members of the Security Council, the United States, China, France, Britain and Russia. The UN is only as effective as its most important members want it to be. The US launched the war in Iraq despite the failure of our own Prime Minister to secure the consent of the UN. China vetoed pressure on the government of Sudan that might end the slaughter in Darfur. The limitations of the office of the Secretary-General are all too apparent.

We are unlikely to see an improvement here until there is a reconfiguration of the Security Council. The Council reflects the world of 1945 not 2007. But there is little evidence that the present incumbents are ready to see their power diluted. We must sadly conclude that the present deadlock is likely to continue.

Yet, despite this, the UN remains the world's best hope of just global governance. As Mr Annan said in his valedictory address, the organisation should ideally be forum where the poor and weak can have some influence over the actions of the rich and powerful. We must judge Mr Ban on the extent to which he can continue the work of his predecessors in turning this noble ideal into a reality.