Britain on Thursday ordered the deportations of seven men detained as threats to national security, including some accused in a terrorist plot to spread the poison ricin.

The men were being held in London and Manchester (search) under the government's powers to deport people "whose presence in the U.K. is not conducive to the public good for reasons of national security," the Home Office said.

Officials declined to disclose the names or nationalities of the seven, but a senior government official told The Associated Press that some them had been charged with planning an attack uncovered two years ago involving ricin, cyanide, botulinum and explosives.

Four Algerians were acquitted in that case in April, and prosecutors dropped charges against three other Algerians and a Libyan. The official, who spoke on condition of anonymity because of the sensitivity of the issue, declined to discuss how many of Thursday's detainees were acquitted in the ricin case or their nationalities.

The Home Office declined to say what had prompted Thursday's deportation orders. However, in recent months the government has been trying to reach agreements with several countries, including Libya and Algeria (search), guaranteeing that detainees would not be tortured or mistreated if deported there.

The only man convicted in the ricin case, Algerian Kamel Bourgass (search), is serving a life sentence for murdering a police officer. He also received 17 years for conspiracy.

Gareth Peirce, an attorney who represented some of the ricin defendants, was unavailable for comment, her office said.

The senior official stressed that the men were detained under the 1971 Immigration Act, not under the new powers introduced last month to deport radical Islamic preachers and others who incite or glorify terrorism. The official said the men were not Islamic clerics.

The poison plot emerged when police raiding an apartment in London two years ago said they found recipes for ricin, cyanide and botulinum and the blueprint for a bomb.

Ricin, derived from the castor bean plant, is one of the world's deadliest toxins and has been linked in the past to Al Qaeda and Iraq. It has no known vaccine or antidote and kills cells by preventing them from making proteins.

The seven men will be held in prison pending deportation proceedings, the Home Office said.

Earlier in August, Britain detained 10 foreign residents, including Omar Mahmoud Othman Abu Omar, also know as Abu Qatada, a radical Muslim preacher previously described by Spanish officials as bin Laden's "spiritual ambassador in Europe."

Britain also barred another radical Muslim cleric, Omar Bakri Mohammed, from returning to the country.

The crackdown followed the July 7 bombings that killed 52 subway and bus passengers and four homicide bombers in London and failed mass-transit attacks two weeks later.

The Home Office said the detainees had five working days to appeal the deportation — a process that could drag on for months.

As a signatory to the European Convention on Human Rights, Britain is not allowed to deport people to countries where they may face torture or mistreatment. Britain has been trying to sign agreements guaranteeing humane treatment of deportees with 10 countries, including Algeria, Lebanon, Egypt and Tunisia. The first such memorandum was signed with Jordan last month.