Five suspected Islamic extremists were held in dawn raids yesterday and face being kicked out of the country as a threat to national security.
Three were detained in the West Midlands, one in London and one in Cardiff in raids by the Immigration Service backed by Special Branch and the Anti-Terrorist Branch.
The foreign nationals were detained using Home Secretary Charles Clarke's powers to deport those whose presence is deemed "not conducive to the public good".
They are being held in prison while efforts to deport them continue. Home Office officials refused to confirm their names or nationalities.
It was the latest step in a Government crackdown on suspected foreign extremists living in the UK.
Ten were detained for deportation in August, including the radical Muslim cleric Abu Qatada, a Jordanian who has been labelled al Qaida's "spiritual ambassador in Europe" by several Western Governments.
Two weeks ago seven more suspected foreign extremists were detained. They included at least three Algerians who were, earlier this year, cleared of involvement in a plot to use ricin poison in London.
All have been detained under the Immigration Act. In the past the Government has been blocked by the European Convention on Human Rights from sending them back to states with poor human rights records, or to where they could face the death penalty. But Ministers have been pursuing changes to protocol which would allow people to be deported to such countries.
The Home Office recently signed a memorandum of understanding with Jordan in which foreign officials pledged not to mistreat or sentence to death those deported from Britain.
It is thought to be close to agreeing a similar arrangement with Algeria.
A spokesman for West Midlands Police confirmed raids there had been carried out using warrants issued under the Terrorism Act.
A Home Office spokesman said: "The Immigration Service detained five individuals. They will be held in secure prison service accommodation."