According to British government documents just made public, Britain took the threat so seriously it drew up a detailed assessment of what the Americans might do, the BBC said.

It was thought U.S. airborne troops would seize oil installations in Saudi Arabia and Kuwait and might even ask the British to do the same in Abu Dhabi.

The British assessment was made after a warning from then U.S. Defence Secretary James Schlesinger to the British ambassador in Washington.

The ambassador quoted Schlesinger as saying "it was no longer obvious to him that the United States could not use force."

The oil embargo was begun by Arab governments during the Yom Kippur war between Israel, Egypt and Syria and was designed to put pressure on the West to get Israel to make concessions.

The embargo was aimed mainly at the United States but many other countries were affected.

There was no military action. The embargo faltered and was ended a few months later, and Israel and Egypt went on to sign a peace agreement.