The head of MI6 discussed the issue in London with Mossad chief Meir Dagan and Saudi officials after British intelligence officers helped to uncover the plant, in the side of a mountain near the ancient city of Qom.

The site is seen as a major threat by Tel Aviv and Riyadh. Details of the talks emerged after John Bolton, America’s former UN ambassador, told a meeting of intelligence analysts that “Riyadh certainly approves” of Israel’s use of Saudi airspace.