The nuclear Non-Proliferation Treaty is one of the most successful pacts ever. Since its signing in 1968, more states have given up nuclear weapon programmes than started them. But it is under fresh strain. Today representatives of some 189 governments meeting in New York will start discussing how to deal with the threats of rogue nuclear states and traders that have emerged since the last treaty review five years ago.

Just as important is how a far smaller band of negotiators fare - officials of Britain, France and Germany who are currently trying to dissuade Iran from following North Korea, which quit the NPT two years ago and proclaimed itself a nuclear weapons state. This negotiation is proving a hard slog; in another inconclusive round of talks in London on Friday, the trio of European governments failed again to get Iran to stop enriching uranium and reprocessing plutonium itself and to rely on outsiders, such as Europe, to supply and recycle its nuclear fuel.