Legal representation, health and other support must be available while people's cases are assessed, a report from the group added.

Prison-style detention should end and be replaced by an open reception unit, the review added. Currently immigrants are sent to detention centres in Great Britain after being brought to a police station.

Liz Griffith from the refugee group said: "Refugees, immigrants and tourists to Northern Ireland are being locked up unnecessarily. The Northern Ireland Executive and Assembly should lobby the Home Office to put in place practical alternatives to detention."

Robin Wilson interviewed eight people caught up in the immigration system for his report, "Distant Voices, Shaken Lives, Human Stories of Immigration Detention from Northern Ireland".

These included Lodorice Djouontso, 36, from Cameroon. She estimated that 15 police and immigration officers took part in a 7am raid, which removed her and her baby daughter to a detention centre in Scotland, where they were kept for almost two weeks before being moved to detention in England. She was held for nearly two months in a single room before being returned to Belfast and given three years' leave to remain here.

Ms Djouontso said: "It's not easy when you don't have your freedom. You have no idea how long you will be there. You have no idea."

The Refugee Action Group (RAG) is now calling for an alternative to transferring Northern Ireland individuals to detention in Great Britain.

"If asylum-seekers are conceived simply as embodiments of a stereotyped and mistrusted group, then warehousing them for an indefinite period in a detention centre with a view to removal will make sense, including as a deterrent to others - even if this represents a denial of international obligations under the Refugee Convention," its report said.

"Recognising that they are each unique individuals, who are likely moreover to have complex needs - like the individuals whose stories have been told above - will however favour a more productive, humane and cheaper approach tailored to their situation."