Developed secretly from 1956 after France built a nuclear reactor at Dimona in the Negev desert, the weapons were seen by Israel's first generation of leaders as designed to prevent a second Holocaust - an argument that was translated into a formidable arsenal outside any international controls. Seymour Hersh, the American writer, has reported that the words "Never Again" were welded, in English and Hebrew, on to the first Israeli nuclear warhead. Apocryphal or not, the story hints at the thinking behind the programme.

Israel, unlike Saddam Hussein's Iraq, never signed the nuclear non-proliferation treaty, the 1970 agreement which allows countries to develop civilian nuclear power in exchange for forgoing weapons. These are supposed to be the preserve of the five permanent members of the UN security …