Nuclear non-proliferation treaty 'fraying at the edges'

It is 20 years since the end of the Cold War and yet there are still 23,000 nuclear warheads in the world, 90% of them held by the US and Russia.

Our guest editor Shirley Williams is worried by the risk that nuclear arms still pose to the world. She discusses the problem with Lord Hannay, a former British Ambassador to the United Nations, and Gareth Evans, a former Australian foreign secretary who is now co-chairman of the International Non-Proliferation and Disarmament Commission.