Some of the information from the suspects is said to have been used by MI5 and MI6, the British intelligence services. The admissibility in court of evidence gained under torture is being considered in the House of Lords in an appeal by foreign-born prisoners at Belmarsh jail, south London, against their detention without trial on suspicion of terrorism.

Over the past two years the unmarked Gulfstream has visited British airports on many occasions, although it is not believed to have been carrying suspects at the time.

The Gulfstream and a similarly anonymous-looking Boeing 737 are hired by American agents from Premier Executive Transport Services, a private company in Massachusetts.

The white 737, registration number N313P, has 32 seats.

It is a frequent visitor to American military bases, although its exact role has not been revealed.

More is known about the Gulfstream, which has the registration number N379P and can carry 14 passengers. Movements detailed in the logs can be matched with several sightings of the Gulfstream at airports when terrorist suspects have been bundled away by US counterterrorist agents.

Analysis of the plane?s flight plans, covering more than two years, shows that it always departs from Washington DC. It has flown to 49 destinations outside America, including the Guantanamo Bay prison camp in Cuba and other US military bases, as well as Egypt, Jordan, Iraq, Morocco, Afghanistan, Libya and Uzbekistan.

Witnesses have claimed that the suspects are frequently bound, gagged and sedated before being put on board the planes, which do not have special facilities for prisoners but are kitted out with tables for meetings and screens for presentations and in-flight films.

The US plane is not used just for carrying prisoners but also appears to be at the disposal of defence and intelligence officials on assignments from Washington.

Its prisoner transfer missions were first reported in May by the Swedish television programme Cold Facts. It described how American agents had arrived in Stockholm in the Gulfstream in December 2001 to take two suspected terrorists from Sweden to Egypt.

At the time of what was presented as an ?extradition? to Egypt, Swedish ministers made no public mention of American involvement in the detention of Ahmed Agiza, 42, and Muhammed Zery, 35, who was later cleared.

Witnesses described seeing the prisoners handed to US agents whose faces were masked by hoods. The clothes of the handcuffed prisoners were cut off and they were dressed in nappies covered by orange overalls before being forcibly given sedatives by suppository.

The Gulfstream flew them to Egypt, where both prisoners claimed they were beaten and tortured with electric shocks to their genitals. Despite liberal Swedish laws on freedom of information, diplomatic telegrams on the case released to the media were edited to conceal the complaints of torture.

Hamida Shalaby, Agiza?s mother, said: ?The mattress had electricity . . . When they connected to the electricity, his body would rise up and then fall down and this up and down would go on until they unplugged electricity.?

A month before the Swedish extradition, the same Gulfstream was identified by Masood Anwar, a Pakistani newspaper reporter in Karachi. Airport staff told Anwar they had seen Jamil Gasim, a Yemeni student who was suspected of links to Al-Qaeda, being bundled aboard the jet by a group of white men wearing masks. The jet took Gasim to Jordan, since when he has disappeared.

?The entire operation was so mysterious that all persons involved in the operation, including US troops, were wearing masks,? a source at the airport told Anwar.

On another mission, in January 2002, a Gulfstream was seen at Jakarta airport to deport Muhammad Saad Iqbal, 24, an Al-Qaeda suspect who was said by US officials to be an acquaintance of Richard Reid, the British ?shoe-bomber? jailed in America for trying to blow up a flight from Paris to Miami.

An Indonesian official told an American newspaper that Iqbal was ?hustled aboard an unmarked, US-registered Gulfstream . . . and flown to Egypt?, where almost nothing has been heard of him since.

The CIA Gulfstream?s flight logs show it flew from Washington to Cairo, where it picked up Egyptian security agents, before apparently going on to Jakarta to take Iqbal to Egypt.

Another transfer involved a British citizen. On November 8, 2002, the Gulfstream took off for Banjul in Gambia. On the same day Wahab Al-Rawi, a 38-year-old Briton, was among four people arrested at the airport by local secret police and handed over to interrogators who said they were ?from the US embassy?.

Wahab said he had previously been questioned by MI5 because his brother Basher, an Iraqi national, was an acquaintance of Abu Qatada, the radical London-based cleric.

When Wahab asked the CIA agents for access to the British consul, as required under the Vienna convention signed by America, the agents are said to have laughed. ?Why do you think you?re here?? one agent said to Wahab. ?It?s your government that tipped us off in the first place.? Wahab was later released but Basher was sent to Guantanamo and remains there and has yet to be accused of any specific crime.

Some former CIA operatives and human rights campaigners claim the agency and the Pentagon use a process called ?rendition? to send suspects to countries such as Egypt and Jordan. They are then tortured largely to gain information for the Americans who, it is alleged, encourage these countries to use aggressive interrogation methods banned under US law.

Bob Baer, a former CIA operative in the Middle East, said: ?If you want a serious interrogation you send a prisoner to Jordan. If you want them to be tortured you send them to Syria. If you want someone to disappear . . . you send them to Egypt.?

Among the countries where prisoners have been sent by America is Uzbekistan, a close ally and a dictatorship whose secret police are notorious for their interrogation methods, including the alleged boiling of prisoners. The Gulfstream made at least seven trips to the Uzbek capital.

The details bolster claims by Craig Murray, the former British ambassador, that America has sent terrorist suspects from Afghanistan to Uzbekistan to be interrogated by torture.

In a memo, whose disclosure last month contributed to Murray?s removal, he told Jack Straw, the foreign secretary, that the CIA station chief in Tashkent had ?readily acknowledged torture was deployed in obtaining intelligence?.

The CIA and Premier declined to discuss the allegations over the planes. The American government, however, denies it is in any way complicit in torture and says it is actively working to stamp out the practice.

Thanks to Bob Lee for passing this article along. --BL