Concern over The Verne immigration removal detainees
Concerns are being raised about the effects of detention on men held at an immigration removal centre in Dorset.
There are nearly 500 men at The Verne in Portland and campaigners say many have little or no indication about how long they will be there.
The Verne Visitors Group said the indefinite nature of detention caused "despair and distress" and was against British principles of justice.
The Home Office said it detained people for the minimum time possible.
The visitors group, which offers support to detainees, said men were typically held for issues such as expired visas or were failed asylum seekers, while others were criminals awaiting deportation.
Chairman Charles Campion-Smith said: "It's the indefinite nature we are particularly concerned about. Detention is an extreme response - depriving people of their liberty who are not criminals in most cases.
"The regime at Portland is humane so our criticism is not of those who implement the policy."
'Dignity and respect'
He said detainees sometimes questioned whether "life was worth living".
"We hope some will feel affronted that people are held indefinitely, without trial and that's against many principles of British justice."
A Home Office spokeswoman said: "Detention and removal are essential parts of effective immigration controls but it is vital they are carried out with dignity and respect.
"When people are detained, it is for the minimum time possible and the welfare of those in our care is of the utmost importance.
"No-one is detained indefinitely and the law is clear that the detention power can only be exercised if there is a reasonable prospect of removal within a reasonable timeframe.
"Individuals are able to apply for immigration bail and challenge their detention in the courts."
The visitors group is holding a public meeting at Dorchester's Corn Exchange at 19:00 GMT.