Despite the opposition of his own generals and widespread scepticism that America is ready to risk the military, political and economic consequences of an airborne strike on Iran, the president has given an “amber light” to an Israeli plan to attack Iran’s main nuclear sites with long-range bombing sorties, the official told The Sunday Times.

“Amber means get on with your preparations, stand by for immediate attack and tell us when you’re ready,” the official said. But the Israelis have also been told that they can expect no help from American forces and will not be able to use US military bases in Iraq for logistical support.