The four were arrested on suspicion of involvement in terrorism immediately after they arrived at a British air base late Tuesday and were taken to a police station in west London. A fifth man was released after being questioned briefly by immigration officers at the air base.
Metropolitan Police said the four men being held in custody at the high security Paddington Green station would be questioned individually by officers from its Anti-Terrorist branch.
Each of the men — Ruhal Ahmed, Tarek Dergoul, Asif Iqbal and Shafiq Rasul — were arrested under a section of the Terrorism Act that concerns alleged involvement in the commission, preparation, or instigation of terrorist acts. Police gave no further details.
All four were examined by a forensic medical examiner to ensure they were fit to be detained and interviewed by police. They were allowed a telephone call and access to lawyers of their choice.
"I welcome the fact that these men are no longer in legal limbo," said Charles Kennedy, leader of the opposition Liberal Democrats party. "Two years without proper recourse to lawyers or access to their families was too long."
Some legal experts doubt there will be enough evidence to try any of the returnees because information gleaned from interrogation at Guantanamo would be inadmissible in court.
The fifth man, 37-year-old Jamal al-Harith, was given a police escort to an undisclosed location after his release.
Al-Harith's lawyer, Robert Lizar, said his client wanted the U.S. authorities "to answer for the injustice which he has suffered."
"He has been detained as an innocent for a period of two years. He has been treated in a cruel, inhumane and degrading manner, he wants the authorities to answer for that," Lizar added.
The five were released from the U.S. Navy prison in Cuba after months of talks between British and American officials, including President Bush and Prime Minister Tony Blair, who discussed the detentions when Bush visited London in November.
"The return of the five British prisoners diffuses tension with Prime Minister Tony Blair," said international law professor and CBS News Foreign Affairs Analyst Pamela Falk. "But the immediate release of one of the men by British authorities appears to strengthen the argument that even suspects picked up in a war on terror should be given basic due process rights that U.S. and international law requires.
"By returning two of the named petitioners in an upcoming Supreme Court case, the Bush Administration may be trying to take some wind out of their opponents' sails," Falk said, "but it may work the other way and the Court may see the releases as demonstrating an arbitrary approach without a legal foundation."
Four Britons remain at Guantanamo — Moazzam Begg, Feroz Abbasi, Richard Belmar and Martin Mubanga. Begg and Abbasi had been listed as some of the first detainees likely to face a military commission, a possibility Britain has criticized and negotiations over their fates will continue.
About 640 prisoners are held at Guantanamo on suspicion of links to Afghanistan's fallen Taliban regime or the al Qaeda terror network.