Some of the men, all Algerians, had earlier been acquitted in a two-year-old plot to perpetrate terrorist attacks in Britain using explosives and a number of poisons, including ricin.
The case has raised concerns among some rights activists. Doug Jewell, of Britain's National Council for Civil Liberties, said the so-called "ricin plot" was specious to begin with. Now, he said, it is unfair to detain and deport men who have not been convicted of terror-related crimes.
"At the present time, the message being sent by this action is that if you are innocent of crime, you will not be acquitted," Jewell said. "You will merely be deported to a country like Algeria, which has a record of torture."
The "ricin plot" case proved a minor embarrassment for the Home Office, which was able to secure the conviction of only a single suspect. But even opposition politicians say the error should not prevent the current detainees from being deported.
Patrick Mercer, a Conservative Party member who serves as a Home Office shadow minister, called the ricin case a "fiasco," but said his party shares the government view that the men should be deported because of their previous criminal records.
The government has sought agreements from countries like Algeria that they will not torture returnees from Britain. Now, Mercer said, the extradition will prove an interesting "test case" for the government.
"It will be interesting to see whether they can be extradited under the agreement that has now been reached with Algeria and that will legally work," Mercer said. "I hope that's the case. These are dangerous men, and I believe we should get rid of them from this country."
The arrests coincided with the government's publication of new security laws, which have prompted strong debate between ruling and opposition politicians. But Mercer said on issues of terror, the two sides find more common ground than usual.
"First and foremost, I think it's important to understand that British politics is normally antagonistic," Mercer said. "But at this stage we in the opposition are trying to help the government get through terrorist legislation. Obviously, above and beyond everything else, [we are thinking about] the good of the country, rather than any political gain."
Mercer stresses, however, that the main sticking point has been the government's proposal to detain suspects for up to three months prior to a court trial.
He said such a step is counterproductive and could cause a sharp public backlash in cases where the suspect is then released without charge because of a lack of evidence.
"If that individual goes back into the community, and can say to subversives or potential terrorists, 'Look, I have been deprived of my freedom for three months without any reason,' that is a very powerful recruiting tool for the terrorist organizations," Mercer said.
Jewell agreed. He said the current two-week detention period should be sufficient for court charges to be prepared.
Some terror experts argue the three months are needed in order to decipher suspects' computer codes in order to find incriminating evidence.