Tuesday the four Britons touched down on British soil at 5:02 p.m., after a battle by their families to secure their release. They had been picked up from Guantánamo Bay, land controlled by the United States on Cuba’s southeast tip, and flown directly to RAF Northolt, London.

Abbasi, 24, is the only one allegedly detained on the battlefield, in Afghanistan in December 2001. Richard Belmar, 25, and Moazzam Begg, 37, reportedly were arrested in Pakistan, while Martin Mubanga, 32, was detained in Zambia.

The fresh allegations of abuse of British detainees and their suffering came from Gitanjali Gutierrez, the U.S. lawyer for Abbasi. Gutierrez met with Abbasi, who comes from Croydon, south London, in Guant´namo last week, where he alleged that he was kept in isolation for 18 months in a windowless cell, he could not go outside to exercise, guards were removed to deny him any human contact (and monitored him by a remote camera), he was repeatedly injected with an unknown substance that triggered psychosis and he feared he would be beaten if he refused to comply with his captors.

Gutierrez, whose comments are subject to censorship by the U.S. military, told the Guardian her client was showing clear signs of the debilitating post-traumatic stress disorder and suffering panic attacks. She said: “The time in isolation led to mental breakdowns, he was talking to himself, hallucinating, sitting in the corner.

“We talked about the difficulties of reintegrating into regular life after the abuses and isolation he suffered. He had periods of psychosis that corresponded with the injections.” Three British detainees released last year also said they had been given mystery injections.

After touching down on British soil the four Britons were arrested under Section 41 of the Terrorism Act of 2000, suspected of involvement in the commission, preparation or instigation of acts of terrorism.

Sir John Stevens, the metropolitan police commissioner who made the decision to arrest, said: “The intelligence and the information was put to me over the weekend,” he said. “I have no other option but to arrest them. If their answers are satisfactory, then they will be released as soon as we can arrange it.” Police said they would be medically examined before interrogation. Because of the “unique circumstances” a family member would be allowed to see them, probably Wednesday. Muslim groups and the men’s families condemned the arrests.

Intelligence officials suggested Tuesday that there was no evidence any of the four presented a security threat. They expected all four to be released quickly, but insisted that the length of detention was up to the police. Muslim leaders who met with Britain’s top anti-terrorism officer, assistant commissioner David Veness, claimed he said the men would only be charged if they admitted criminal acts.

The four have been questioned at Guantánamo Bay up to nine times by MI5 officers. Any intelligence relevant to the war on terror would have been acted on already by Britain or the United States, anti-terrorism officials suggest. The four flew back to Britain on an RAF-C-17 military aircraft, accompanied by Scotland Yard anti-terrorist officers and two independent observers, one a Muslim. Police videoed the flight to guard against claims of ill treatment.

Up to 550 Muslim men remain in Guantánamo, including at least six British residents whom the government has declined to represent.

Detainee Moazzam Begg alleges he was suspended by handcuffs from a bar and threatened with death. Martin Mubanga says that he was shackled for so long that he wet himself. All the detainees were interrogated repeatedly, and they had barely an hour of exercise a week.

The allegations that have already emerged from these four Britons echo those made by some of the five Britons who were released in March 2003. The so-called Tipton Three produced a dossier alleging that techniques employed by the United States to break them included repeated beatings, shackling them to the floor for long periods, the use of loud music, questioning them at gunpoint and exposure to extremes of hot and cold.

Washington and London hope the issue of Guantánamo Bay will fade away once the men have been released. The issue has poisoned relations between the two close allies, and embarrassed British Prime Minister Tony Blair.

Britain’s attorney general, Lord Goldsmith, spearheaded the effort to negotiate a deal for the men’s release. The United States had wanted them to face military commissions whose rules, critics said, were rigged in favor of the prosecution. After pressure from supporters of the detainees, senior ministers condemned the planned trials and last March secured the release of five of the Britons held there. But the United States held on to four. The failure to secure their release led to the value of Blair’s special relationship with George W. Bush being questioned, with the continued incarceration serving as a symbol of Blair’s impotence.

Tuesday’s announcement of the detainees’ imminent release raised questions about why the Bush administration had finally agreed. U.S. Defense Secretary Donald Rumsfeld had claimed that those held in Guantánamo were the “hardest of the hard”; now the Britons are to be sent back to the U.K. and almost certain freedom.

Eugene Fidell, president of the U.S. National Institute of Military Justice, is in no doubt about the reason: “They would have been charged if the government had any evidence on them. The purpose of these detentions is to squeeze people for information, not to prosecute them.”

In the United States, the free run the Bush administration had enjoyed in its treatment of up to 680 Muslim men at Guantánamo came to an end last summer. In June the Supreme Court struck down the president’s claim that Guantánamo was not under the jurisdiction of U.S. courts. The ruling meant that detainees could sue the government to force it to justify their detention, and lawsuits were launched. U.S. government lawyers have so far failed to have the cases struck down. As Fidell said: “The credibility of Guantánamo is extremely low. The government has lost every legal battle that has occurred concerning the detentions.”

In the United States FBI documents have emerged showing the agency’s concern about how detainees were being treated. Former Guantánamo interrogators told the New York Times that ill treatment was used or threatened at the prison, and the Pentagon was forced to announce an inquiry into the allegations of abuses.

Brent Mickum, the U.S. lawyer for Mubanga, said concern had been growing: “The Bush administration has realized it is hurting them now. These hideous allegations are established; it is not an anti-terrorism facility, it is a torture facility. The government can’t deny the torture anymore because it is their own documents, from the FBI, saying this. Rather than letting all these people parade through the courts saying they were tortured or ill-treated, they let them go.”

In Britain, the situation at Guantánamo was condemned by Tory M.P.’s and people on the left; in the United States, some Republicans attacked the system, as did military officers assigned to defend the detainees picked to face trial before military commissions. It was also another reason for Muslim Labor voters to desert Labor.

Iqbal Sacranie, secretary general of the Muslim Council of Britain, said whenever he and his members met with senior ministers the issue of Guantánamo had been raised: “We made clear that this was a crucial issue for British Muslims, who feel since 9/11 laws are being applied to them in a discriminatory manner. Guantánamo symbolized how Muslims feel they are being treated.” Tuesday the government felt some relief that finally the last British citizens were on their way home.

The action was brought by the so-called Tipton three — Shafiq Rasul, Asif Iqbal and Rhuhel Ahmed — and Jamal al-Harith from Manchester, England. All deny links or involvement in terrorism. The lawsuit alleges that the Britons were “repeatedly struck with rifle butts, punched, kicked and slapped. They were short-shackled in painful stress positions for many hours … causing deep flesh wounds and permanent scarring. Plaintiffs were also threatened with unmuzzled dogs, forced to strip naked, subjected to repeated forced body-cavity searches, intentionally subjected to extremes of heat and cold for the purpose of causing suffering.”

The lawsuit claims the mistreatment was “in plain violation” of the U.S. Constitution, federal law and its international treaty obligations. The Britons say the highest levels of the U.S. government are to blame for their torture: “It was the result of deliberate and foreseeable action taken by defendant Rumsfeld and senior officers to flout or evade the U.S. Constitution … law … treaty obligations and long established norms of customary international law.”

In a December 2002 memo, Rumsfeld authorized the “use of mild, non-injurious physical contact, such as grabbing, poking in the chest with the finger and light pushing.” Also approved were stress positions, isolation for 30 days, deprivation of light and other stimuli, 20-hour interrogations, convincing detainees that death or severe pain was imminent, shaving the beards of Muslim men and using dogs.

In one declassified U.S. document, a lawyer advises that “the use of a wet towel to induce the misperception of suffocation would also be permissible.”

In August, the Tipton three released a 115-page dossier detailing their alleged ill treatment. The Red Cross said the allegations were so serious that, if true, they amounted to war crimes. Eventually, one of the Tipton three confessed to meeting Osama bin Laden at an al-Qaida training camp. But British intelligence established that he was working in a Currys electrical store in the U.K. at the time.

In a statement Wednesday, the three said: “We believe those who have been and still are responsible for these deliberate and unlawful actions must be held accountable. If they are not, this nightmare will happen again and again to others.” The U.S. government is expected to try to get the case thrown out or to argue that the actions of senior officials are immune from prosecution because the U.S. was “at war” after the Sept. 11 attacks.