The United Nations Secretary General Kofi Annan has insisted that the Security Council would have to be enlarged beyond the five permanent members or it would lose credibility.
Annan said on Tuesday that one of the "great failures" of the World Summit in New York in September was that it did not reach an agreement on enlargement.
He said it could hamper progress towards reform.
The Security Council has 15 members: five permanent members with the right to veto -- Britain, China, France, Russia and the United States -- and 10 elected by the General Assembly for two-year terms.
India, Brazil, Germany and Japan have joined forces to press for a permanent seat each on the Council.
"Although the UK supported enlargement, I suspect that in London, as in other capitals of existing permanent members, not many tears are shed over this failure," Annan said.
"But do not underestimate the slow erosion of the UN's authority and legitimacy that stems from the perception that it has a very narrow power-base, with just five countries calling the shots.
"It is this feeling of frustration and exclusion that prompts many states to exercise the only power they do have: the power to block other reforms, such as better management -- since some see even this as an attempt by the big boys to grab yet more power for themselves.
{{/usCountry}}"It is this feeling of frustration and exclusion that prompts many states to exercise the only power they do have: the power to block other reforms, such as better management -- since some see even this as an attempt by the big boys to grab yet more power for themselves.
{{/usCountry}}"So the base must be broadened. Sooner or later, the Security Council will have to be enlarged. But meanwhile there are other ways to give more states more of a say in UN decisions," Annan said.