The reporter is accusing the US President George Bush of 'science fiction' politics over his attitude towards Iraq and possible attacks against neighbouring Iran.

Pulitzer Prize-winning Hersh - who also exposed the Abu Ghraib prison torture scandal - says Bush is trying to convince his people that Iran is behind the insurgency in Iraq.

He says there's no guarantee that Mr Bush won't go to war against Tehran before he leaves office:

"What we have now is operational planning. This is serious.

"They have done their targeting, they've done everything they need.

"They've limited the planning to try and get support from our allies, including the UK."

Prime Minister Brown will have to decide how far British support will go. An all-out assault plan on Iran's nuclear facilities is said to have been ripped up by the Pentagon. In its place is said to be limited precision bombing of key facilities.

Hersh stated that: "The bombing plan has had its most positive reception from Gordon Brown."

Neither the Pentagon nor Downing Street say they recognise the assessment.