Yesterday, US President Barack Obama chaired a summit of the UN Security Council to discuss nuclear disarmament and non-proliferation. This is one of the most critical issues we face. Get it right, and we will increase global security, pave the way for a world without nuclear weapons and improve access to affordable, safe and dependable energy — vital to tackle climate change. Get it wrong, and we face the spread of nuclear weapons and the chilling prospect of nuclear material falling into the hands of terrorists.

Ministers from the E3+3 (Britain, France, Germany, China, Russia and the US) will also meet ahead of talks with Iran on October 1. Iran has said it wants only to assert its rights under the non-proliferation treaty, but its refusal to come clean about its past nuclear activities has caused deep concern in the international community. Iran is not the victim of Western bias. The E3+3 has made a very clear and strong offer. We have even offered to help Iran develop a civil nuclear programme. We have long urged Iran to respond positively to this offer. Now is the time to do so.

With this week's Security Council summit and, next May, the review conference of the Nuclear Non-proliferation Treaty, we have a historic opportunity to make progress across the entire nuclear agenda. What do we need to do? In July, British Prime Minister Gordon Brown set out a detailed strategy for the period up to the review conference and beyond to bring us the security and prosperity we seek in the decades to come. There are five key areas.

First, nuclear power can be an essential part of the solution to climate change and energy security. A growing number of countries are looking at building nuclear power plants. I welcome that. But we need to work together to develop effective international mechanisms, overseen by the International Atomic Energy Agency (IAEA), to help countries realise the benefits of nuclear energy while minimising the risks of nuclear weapons. A number of constructive ideas have been put forward, including most recently by the UK. We are also promoting an innovative partnership between industry, academia and government for research to tackle the technical challenges involved.

Policing

Second, we must strengthen the systems designed to detect any attempt to acquire nuclear weapons and we must ensure that any such attempt has serious consequences. The IAEA again has the central role: its regime of safeguards of nuclear facilities and materials needs to be further strengthened. And countries seeking to withdraw from the non-proliferation treaty must be held responsible for any violations committed before they withdrew.

The world needs to deal firmly with any government that fails to meet its non-proliferation obligations. In clear breach of UN Security Council resolutions, North Korea continues to test missiles and to enrich uranium and has exploded two nuclear devices, while Iran continues to enrich uranium and refuses to answer the most difficult questions about its past programmes. Both North Korea and Iran face clear choices. Their governments can put the needs of their people first, they can join the international mainstream and invest in modern economies that will bring jobs and raise living standards. Or they can face still deeper isolation and tougher sanctions.

Third, terrorist networks such as Al Qaida have made clear their intent to acquire nuclear weapons. It is vital that we ensure they can never do so. This requires stronger, universally implemented international standards to protect nuclear materials. We have warmly welcomed Obama's intention to host a summit on nuclear security issues next April.

Fourth, there are still three countries — India, Israel and Pakistan — which have not signed the non-proliferation treaty. We continue to call on them to join as non-nuclear weapons states. In the Middle East, we support the establishment of a zone free from all weapons of mass destruction.

Finally, we must create the conditions for the eventual elimination of all nuclear weapons. This will be highly challenging. But there are encouraging signs, most recently the understanding between the US and Russia to achieve significant further cuts in their nuclear arsenals, which together make up 95 per cent of the world's total. Progress on treaties underpinning nuclear disarmament — which have too long been stalled — has also recently begun to look more hopeful, with renewed prospects for achieving the entry into force of the comprehensive test ban treaty and for starting negotiations on a treaty to ban the production of fissile material for nuclear weapons or other nuclear explosive purposes.

After a decade of deadlock, there is now genuine cause for optimism that we can move forward into a decade of decisions. Multilateral disarmament has always suffered from the suggestion that it lacked either principle or idealism. We have a chance to show it embodies both, and to signal the international community's intent to take action across the entire range of nuclear issues. By reinvigorating international commitment and working together, we can strengthen our shared security. This week presents an opportunity for the world's leaders to steer us all down a safer path.

David Miliband is the Secretary of State for Foreign and Commonwealth Affairs in the United Kingdom