Around 300 people, many of them refugees and asylum seekers, rallied despite the rain outside Yarl's Wood detention centre in Bedfordshire today.
Rejected asylum seekers, mostly women, are imprisoned there without trial often before being deported.
The demonstration, the latest in a series called at Yarl's Wood by Movement for Justice, came days after the announcement that Dungavel detention centre in Scotland is to close after years of campaigning.
Isha from Senegal told Socialist Worker, "It will take a long time, but we can get rid of the whole detention system - it is possible. It's a matter of justice. I know people who have been detained, it's not right locking people up for nothing."
Neema from Congo said "We come to Britain fleeing persecution only to find a different kind of persecution. You have no peace when you know you can be detained or deported at any moment.
"The government treats people like they aren't human - I'm here to tell them they don't have the right."
Some detainees waved through their windows. One shouted, "thank you for coming," another led a chant of "Shut down Yarl's Wood!"
Several women spoke to the protest from inside over a telephone. In tears one woman said, "I have three children who were born in Britain and need their mother, but still they are trying to deport me."
Some detainees said guards - employed by private contractor Serco - had locked the corridors to stop them coming to the rooms facing the protest.
"They are saying don't shout, don't go to the window," explained one woman.
It shows how solidarity protests outside the bleak, isolated jail are giving the women inside a boost - and putting the wind up the bosses.But they are also part of a broader fight against the racist machinery of immigration enforcement.
Sophie, who is about to start as a student at London Met, said, "The point of being here is to show those inside that they're not alone, and to show the government that hiding detention centres away in places like this won't stop us contesting them.
"It can be quite demoralising to go home at the end knowing they're still stuck in there. So the important thing is to remember where to focus our anger - it's government policy that's to blame. We need system change."