The Ethiopian-born former British resident claimed he was the victim of a dark nightmare of "medieval torture" wreaked on him with British collusion.

He arrived back in Britain at RAF Northolt airbase in north-west London soon after 1pm GMT on Monday (midnight AEDT on Tuesday). He was detained by police officers under anti-terrorism laws but not arrested. After being questioned for nearly five hours, he was released at 5.46pm GMT (4.46am AEDT on Tuesday), police said. Mr Mohamed was in custody since 2002. He was arrested in Pakistan before being taken to Morocco and Afghanistan, and then on to Guantanamo Bay.

He was suspected of attending an al-Qaeda training camp in Afghanistan and plotting to build a "dirty" bomb. But he was never charged.

His US military lawyer, Lieutenant Colonel Yvonne Bradley, said: "Mr Mohamed has not done anything that warranted any investigation." Looking underweight, stooped and hiding behind a white baseball cap, Mr Mohamed shuffled off the chartered jet clutching what looked like a large collection of documents. Mr Stafford Smith told reporters at the airbase Mr Mohamed was reunited with his sister, whom he had not seen for seven years. "It was a tearful reunion," Mr Stafford Smith said, describing his appearance as "incredibly skinny" and "very emaciated". "He just wants to go to a place we've got for him tonight where he can be by himself with his sister and hopefully begin to put his life together again."

Hunger strike Speaking at a press conference before Mr Mohamed's arrival, Lieutenant Colonel Bradley said Mr Mohamed had been on a hunger strike for some weeks and was in poor mental and physical health. "I know he is fit to travel, but that is pretty much a minimum status for him," she said. "I know he is going to have to put on a lot of weight as he was at least 40 to 50 pounds underweight when I last saw him. [Recovering] mentally is going to be a longer process, given the ordeal that he has gone through." However, in an emotional written statement released before his arrival by his lawyers, Mr Mohamed thanked those in Britain who had worked to gain his release since he was arrested. But he also described the pain of betrayal by the nation he had adopted as his own. "I have to say, more in sadness than in anger, that many have been complicit in my own horrors over the past seven years ... for myself, the very worst moment came when I realised in Morocco that the people who were torturing me were receiving questions and materials from British intelligence, " he said.

"I had met with British intelligence in Pakistan. I had been open with them. Yet the very people who I had hoped would come to my rescue, I later realised, had allied themselves with my abusers." Mr Mohamed said he did not feel up to facing the media immediately after his arrival and, while he wanted to concentrate on regaining his health, he wanted to help those he left behind. "While I want to recover, and put it all as far in the past as I can, I also know I have an obligation to the people who still remain in those torture chambers ... my own despair was greatest when I thought that everyone had abandoned me. I have a duty to make sure that nobody else is forgotten," he said.

"Before this ordeal, 'torture' was an abstract word to me," he said. "I could never have imagined that I would be its victim. It is still difficult for me to believe that I was abducted, hauled from one country to the next, and tortured in medieval ways - all orchestrated by the US Government."

The US has dropped all charges against him. However, while Mr Mohamed will be granted treatment by the British National Health Scheme (NHS), he is not a British citizen and his immigration status will be reviewed.

Prime Minister Gordon Brown said: "We have got to look at the details of the arrangements, but ... we will do everything in our power to protect the security of people in our country and the Home Secretary will take whatever action is necessary.''

It is understood that Mr Mohamed will have to report regularly to the British authorities and has accepted that he will be kept under surveillance. The Attorney-General is now consulting the Director of Public Prosecutions over whether to order a criminal investigation into Mr Mohamed's claims British agents colluded in his torture. All nine British nationals held in Guantanamo were released in 2004 and 2005. Of the six British residents, four were released in 2007.

Following Mr Mohamed's release, the one British resident remaining in the detention camp is Shaker Aamer. "We have requested from the US an offer of release and return [for Aamer] but the US Government has so far declined to agree on his return to the UK,'' a Foreign Office spokesman said.

Loading Paola Totaro is the 's Europe Correspondent.