How important is a nuclear deterrent in the 21st century?
In a HARDtalk interview broadcast on 29 August, Stephen Sackur talks to Sir Michael Quinlan about the state of global security and international relations.
There was a time when global military strategy was relatively straightforward.
The Soviet bloc and the West faced each other with nuclear arsenals and relied on the deterrent effect of mutually assured destruction.
Sir Michael Quinlan was Britain's top official in the Ministry of Defence when those certainties came to an end.
A decade and a half later does Britain need its nukes, and can Iran be stopped from getting them too?
HARDtalk can be seen on BBC World at 0330 GMT 0830 GMT 1030 GMT 1430 GMT 1830 GMT 2330 GMT
It can also be seen on BBC News 24 at 0430 and 2330