By James Blitz, defence and diplomatic editor

Something remarkable has happened in the international negotiations with Iran over its nuclear programme. It is this.

For the past five years, Iran has often looked like a sharp and canny player of the diplomatic game, regularly dividing the US and Russia with its tactics, cleverly making concessions to negotiators in order to buy time, frequently rattling its opponents. Iranian diplomats have often seemed to me to be the sort of people you wouldn’t want to play chess with. They are master tacticians, who know full well how to confuse their adversaries.