Revelations about the contents of the so-called “secret annexe” change little in diplomatic efforts to force a halt to Iran’s nuclear programme. But they do give an insight into some of the questions that Iran must answer if it is to dispel well-founded suspicions that it is, at the very least, putting in place the facilities and expertise to build itself a nuclear bomb.

Iran’s next international appointment is on October 19, when it meets with nuclear officials from the US, Russia and France to discuss a deal to transfer overseas almost 90 per cent of its known stockpile of enriched uranium for reprocessing.

That agreement, struck in Geneva, will allay temporarily fears that Tehran could divert nuclear fuel to a weapons programme. The catch, of course, is whether it has secret stockpiles elsewhere.

On October 25, inspectors will travel to the Republican Guard base near Qom to examine the recently unveiled enrichment plant. What they find could prove crucial to how the world then deals with Tehran. Western powers believe that the site is part of a military nuclear programme, a belief bolstered by its size, clandestine nature and location on a heavily guarded base.

Why inspectors must wait three weeks to see it remains unclear and may fuel suspicions about a “clean-up” ahead of the visit. Given that the site is far from operational, the inspection may prove inconclusive.

Before October is out, another round of talks is planned with Iran. The E3 plus 3 (Germany, France, Britain, China, Russia and the US) will be looking for evidence that Tehran is truly co-operating.

Iran’s behaviour in Geneva last week was encouraging but is still far short of the enrichment freeze that is being demanded if no new sanctions are to be imposed.

Tehran has until the end of the year to decide how far it is prepared to go.

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