Iran and the international community have agreed a four- month extension to the deadline on finding a mutually agreed solution to the standoff over Iran’s nuclear programme and the talks will now restart in September, with a final deadline set for November 24. The process will not be easy and a joint statement from EU foreign policy chief Catherine Ashton and Iran’s Foreign Minister Mohammad Javad Zarif said that “there are still significant gaps on some core issues which will require more time and effort”.

But the extension is not in itself an indication of failure, and merely shows that the negotiations have not gone as fast as they might have done. Nonetheless, the extension obviously gives an opportunity to those like the Republicans and Israelis who want the talks to fail. But the fact is that the two sides have come very much closer than they were at the start and there is a fair chance they can meet in the middle. The crunch issue is how much capacity should Iran have to enrich uranium, which for years Iran has insisted that is its right under the Non-Proliferation Treaty to supply material for power plants and medical research. The Americans only agreed to recognise this right last year.

Now the argument is a debate over numbers, with the P5+1 (permanent members of the UN Security Council plus Germany) saying that Iran should have between 500 to 1,200 centrifuges, while Iran actually has just under 10,000. Supreme Leader Ayatollah Ali Khamenei has muddled matters by claiming two weeks ago that Iran needed the equivalent of 190,000 first generation centrifuges. However, if this argument over numbers gets stuck, it is possible to change the dialogue completely and use a new metric. For example, it would be perfectly possible to have a very good deal based on measuring how many kilos of enriched uranium Iran should have, rather than the number of centrifuges.

All the politicians on both sides need to work to keep calm and find a successful way through these very tortuous negotiations.