Wahab al-Rawi, whose brother Bisher has been held in the US naval base in Cuba for three years, says that US interrorgators told him the British were directly responsible for his arrest and detention. The new claims confirm previous allegations that Britain has played a major role in the "extraordinary rendition" of terror suspects by handing them over to the Americans without legal authority.

In his first interview since his arrest in November 2002, Mr al-Rawi says soon after his detention he asked to see someone from the British High Commission in Gambia but was told by the Americans: "Who do you do think ordered your arrest in the first place? They don't want to talk to you."

Mr al-Rawi claims that the only reason he and another man were allowed to return to Britain after 28 days of questioning by US intelligence officers was because they could claim British citizenship. His brother, Bisher, and Jamil el-Banna, both residents in Britain, were flown to Bagram air base in Afghanistan before being transferred to Guantanamo.

Intelligence reports made by MI5 which have been submitted to the all-party group on extraordinary rendition support Mr al-Rawi's testimony and show the weakness of the case against the four men.

Part of this evidence, which was passed on to the Americans, includes allegations that Bisher al-Rawi had an interest in "extreme sports" while Wahab was described as playing a lead role in setting up a peanut-processing factory in the Gambia. MI5 "intelligence" on the men also revealed that they carried copies of the Koran and had had an electronic device which turned out to be an ordinary battery charger.

Bisher al-Rawi, 38, and Wahab, 40, came to this country in the early 1980s after their father fell under the suspicion of Saddam Hussein. They lived in Cambridge where they took their O-levels before continuing their schooling at Millfield School, Somerset, and Concord College, Shropshire.

They later attended separate universities. Wahab read mechanical engineering at Salford and Bisher read material engineering at University College London. In 1992 Wahab took British nationality while his brother decided to retain his Iraqi citizenship as he did not want to damage his ties with his home country.

It was Wahab's business interests that brought the two brothers to Gambia in November 2002. "I had this business idea for a mobile peanut-oil processing factory," he told The Independent. "I had done the feasibility study, it was all ready to go. I had my team and we brought Bisher in on the deal towards the end."

From the start there were ominous signs that the trip was not going to be straightforward. On the day of his departure flight, Wahab was detained at City Airport in east London by two men who described themselves as airport security officers but whom Wahab suspected of being MI5 officers.

The men wanted to find out about an alleged terror suspect called Abu Qatada whom Wahab had known for many years and had met four days before his flight. Mr Qatada is now imprisoned in Britain as a terror suspect and was once called Osama bin Laden's spiritual representative in Europe. The brothers had come to rely on him as an authority on Islamic law and that was why Wahab had gone to see him. "I needed to know whether, under Islamic law, it was allowed for partners in a firm to be paid wages - he told me it wasn't and so I thanked him and left."

Four days after Wahab had arrived in Gambia he went to Banjul airport to meet his brother, Mr el-Banna and Abdullah el-Ganudi, a British citizen.

Three days earlier, the three men had been arrested at Gatwick airport when they first tried to fly out to Gambia. They were taken to Paddington Green police station in west London on suspicion of carrying an explosive device which turned out to be the harmless battery charger. It was the intelligence obtained from these interviews and searches that was passed on to Gambian and US authorities.

As Wahab approached his brother at Banjul airport he became aware of a problem with immigration. Gambian officials had confiscated their passports and they were being taken to an interview room.

"They began by saying there was an irregularity with their visas. But it became clear it was more than that because they took us to the headquarters of the Gambian National Intelligence Agency in Banjul. We were questioned by Gambians for a few hours before being moved to another room where two US officers took over," says Wahab. "I'm afraid I lost my temper and demanded to see the British High Commissioner and my lawyer. They said it was much too late for that."

For the next three to four days the four men were moved around the building from room to room, alternately questioned by Americans and Gambians.

Says Wahab: "I agreed to answer the Gambian questions but refused to answer any of the Americans'. I was scared but didn't know why I should co-operate."

Four days after Wahab had met Bisher at the airport they were taken from the NIA headquarters to a secret location in the Banjul suburbs. It was here that Bisher begged his brother to co-operate with the Americans because "we have nothing to hide."

"We were all in the house," Wahab said, "and during a break from interrogations Bisher told me to stop being difficult and answer the questions so we could all be sent back home. So I did. I agreed to tell them all about the business we were planning and why we were in Gambia."

Mr el-Janudi and Wahab were separated from the other two and taken back to interrogation suites in the NIA building where the Americans began repeating the questions.

"After I had answered their questions about the trip they started accusing me of coming to Gambia to start a training camp for a terrorist campaign against American targets. It was at this point that I withdrew my co-operation because the questioning was getting ridiculous. Once again I demanded to see someone from the High Commission. This was when they said: 'Who do you do think ordered your arrest in the first place? They don't want to talk to you.' Now it was clear we had been set up and betrayed by the country we had adopted as our own."