When tensions are running high throughout the Middle East and between Tehran and Washington, the question of how far forward Iran is with its nuclear programme could barely be more important.

The answer depends on who you ask – and what their political agenda is. One group emphasises the speed of Iran’s progress, to justify rejection of the current strategy of incremental sanctions designed to persuade Tehran to rein in its programme. The other plays down Iran’s development, insisting there is plenty of time for the slow-acting sanctions to change Iran’s behaviour.