In a chilling scenario of how war might come, a senior intelligence officer warned that public denunciation of Iranian meddling in Iraq - arming and training militants - would lead to cross border raids on Iranian training camps and bomb factories.

Under the theory - which is gaining credence in Washington security circles - US action would provoke a major Iranian response, perhaps in the form of moves to cut off Gulf oil supplies, providing a trigger for air strikes against Iran's nuclear facilities and even its armed forces.

The vice president is said to advocate the use of bunker-busting tactical nuclear weapons against Iran's nuclear sites. His allies dispute this, but Mr Cheney is understood to be lobbying for air strikes if sites can be identified where Revolutionary Guard units are training Shia militias.

The source said: "When you go down there and see the body language, you can see that Cheney is still The Man. Condi pushed for diplomacy but she is no dove. If it becomes necessary she will be on board. "Both of them are very close to the president, and where they differ they are working together to find a way to present a position they can both live with."

The Sunday Telegraph has been told that Mr Bush has privately promised her that he would consult "meaningfully" with Congressional leaders of both parties before any military action against Iran on the understanding that Miss Rice would resign if this did not happen.