The intercepted top-secret fax contained information that America never wanted the world to know -- that the US was holding war-on-terror captives at clandestine "black site" prisons in eastern Europe.
The fax, datelined November 10, 2005, 8.24pm, was sent by the Egyptian foreign minister, Ahmed Aboul Gheit, in Cairo, to his ambassador in London.
It revealed that the US had detained at least 23 Iraqi and Afghani captives at a military base called Mihail Kogalniceanu in Romania, and added that similar secret prisons were also to be found in Poland, Ukraine, Kosovo, Macedonia and Bulgaria.
The discovery of the fax seriously undermines the US's denial that it has ever used secret detention facilities, breaching international law.
It also adds to the pressure for the release of information on "extraordinary renditions".
These rendition flights see kidnapped terror suspects taken by the CIA to countries where torture is common, such as Uzbekistan. British intelligence has supported this practice and UK airports, particulary Prestwick, have given CIA jets logistical support.