Last October's Tehran agreement between Iran and the foreign ministers of the big three European powers - Britain, France and Germany - was hailed at the time as a breakthrough. This was not just for the cause of nuclear non-proliferation but for diplomacy itself. Old Europe, it was claimed, had showed Washington how a hostile regime in the Middle East could be turned by negotiation, rather than invasion, back to the path of peace.
This claim has proved somewhat premature. What the inspectors of the International Atomic Energy Agency found when they were finally allowed into Iran's nuclear facilities was a programme of uranium enrichment - the process essential to manufacturing bomb-grade material - substantially more advanced than they had bargained for.
Iran's nuclear glasnost had not lessened European suspicions that Tehran had been trying to make a nuclear bomb. It had increased them. Iran, for its part, felt betrayed by the fact that Europe had not stuck to the deal. Iran was still regarded as the bad boy, high on the IAEA's agenda.
Last month, Iran wrote to the European Union troika to say that the deal was off. It would resume manufacturing parts for centrifuges that refine crude uranium into the material, which it continues to claim, it needs for its civilian nuclear power programme.
On Tuesday it was revealed that Iran has restarted building the centrifuges and as diplomats from the three European countries and Iran sat down in Paris yesterday, room for manoeuvre appeared to have narrowed even further.
Iran had begun testing equipment used to make uranium hexafluoride, the gas which can be enriched when injected into the centrifuges.
The gap between the two sides is so wide that officials are pessimistic about their ability to bridge it. While intent on resisting pressure from Washington for a UN resolution and sanctions, British officials know that they are playing a waiting game.
The IAEA is due to report in August, but will try to keep the ball in play until after the presidential election in November. The Bush administration has made little secret of its desire to target Iran next, by fermenting the reformist opposition, a prospect which democrats in Iran must dread.
The big question is how far Tehran will go. Will it feel emboldened by the fact that Washington has rid it of its two worst regional enemies in Saddam and the Taliban, and pursue a bomb as the only effective insurance policy against regime change, or will it draw back from the brink?