British military chiefs took part in a so-called war game to prepare for the possible invasion of Iran - despite Government claims that an invasion of the country is "inconceivable".
Senior officers took part in the US-led exercise, Hotspur 2004, two years ago in Virginia.
Despite the game taking place in a fictional country, Korona, the borders of the country were reported to be exactly the same as Iran's - and the characteristics of the enemy were Iranian.
The game was played out in July 2004 - at a time of accelerated US planning after the fall of Baghdad in case of a possible conflict with Iran.
The Ministry of Defence has claimed the game involved invented countries and situations, but using real maps - and stressed that military action against Iran had been dismissed by Foreign Secretary Jack Straw.
A spokesman said: "These paper-based exercises are designed to test officers to the limit in fictional scenarios."
It is believed US and UK military take part in a wide range of war games. It is understood a game based upon the fictional invasion of Scotland was conducted in January this year.
A Foreign Office spokesman added that speculation about war with Iran was "unhelpful".
