Protests are being held at detention centres around the UK as part of a Europe-wide action for asylum seekers.
Asylum seekers are detained in prison cells
Demonstrators are targeting centres in Yorkshire, Liverpool, Glasgow, Oxford, Hull and London's Eurostar terminal.
Organisers claim refugees are being treated unfairly and detention centres where they are held while applications are processed should be closed.
A Home Office spokesman said: "We do not detain people lightly. Detainees are treated with dignity and decency."
Around 30 members of the Committee to Defend Asylum Seekers are handing out leaflets at the Eurostar terminal, arguing it is one of the main symbols of the British government's "anti-asylum seeker apparatus".
Spokesman Alan Gibson, 57, told BBC News Online: "At any one time, up to 2,268 people who have committed no crime are incarcerated in a new, fast-growing second prison system just for foreigners.
"Asylum seekers, if not detained, are forbidden to work and receive a mere 70% of income support on which to subsist.
"If their claim is rejected even this support is removed. Yet thousands of them have nowhere else to go."
MOST APPLICANTS BY NATIONALITY
Q3 2003 Source: Home Office
He added: "Home Secretary David Blunkett is turning Britain into a place where nobody with a 'foreign' accent or appearance can feel safe.
"We believe it is not possible to make a clear distinction between a political asylum seeker and an economic migrant - someone who has fled their country on economic grounds is just a much a victim of their regime.
"The resources that are being put into hearing asylum cases are also pitiful."
A spokesman for the National Coalition of Anti-Deportation Campaigns, which is protesting at HMP Lindholme, said the 112 detainees there "do not feel safe".
A spokesman claimed detainees were subjected to poor food, heating and healthcare.
He said: "Staff treat detainees as offenders rather than recognising that they have not been convicted of any crime.
"People are imprisoned without charge, time limit or trial, with no proper reason given," the spokesman said.
But a Home Office spokesman denied the accusations, telling BBC News Online: "Detention is used sparingly and for the minimum periods necessary.
"We do not detain people lightly - each case is assessed on its own merits."
Regular independent inspections are conducted at all detention facilities to ensure they "meet the standards we are committed to providing", he added.
"Detainees are treated with dignity and decency and provided with recreational and religious facilities."