Dr Mohamed ElBaradei rarely gives interviews

Its role to police the Nuclear Non-Proliferation Treaty (NPT) has been put under unprecedented pressure by Iran and its determination to have its own nuclear programme.

This BBC Radio 4 two-part documentary charts a critical time for the UN as concern grows about the spread of nuclear weapons.

BBC Reporter and former Berlin correspondent, Rob Broomby has had unique access over the past year to main players in this game of international nuclear brinksmanship.

From the meeting rooms of the IAEA Headquarters in Vienna to the dusty plains of Kazakhstan, he has been allowed to witness the work of the agency at a time when the stakes have never been higher.

The IAEA's role has been put under unprecedented pressure by Iran

In 2003 the IAEA reported that Iran had a secret uranium enrichment programme for nearly two decades.

Broomby opens the current chapter of saga as the UN Security Council passes a resolution, in the summer of last year, calling on the country to suspend uranium enrichment or face sanctions.

He follows Greg Schulte, US ambassador to the IAEA who believes that Iran is trying to develop nuclear weapons.

Broomby also tracks the Iranian ambassador, Ali Asgar Soltaneih through the tense negotiations as both sides raise the stakes.

Rob Broomby got privileged access to the work of nuclear inspectors

He is privy to the inner workings of the IAEA over a period of 12 months as its head of inspections Ollie Heinonen tries to weather the growing diplomatic storm.

He hears a frank assessment of the nuclear threat from its Director General Mohamed ElBaradei.

The journalist was also given a privileged insight into the nerve centre of the IAEA's laboratories that monitor the world's nuclear facilities and has spent considerable time with nuclear inspectors, travelling with them to Georgia and Kazakhstan.

There he discovered the reality of searching for nuclear material that has been hidden or lost and the fear of the "dirty bomb".

Over the two programmes the work of the IAEA is explored as a developing crisis unfolds between Iran and the West over the nuclear issue.