Immigration detainees have launched a legal challenge over a Home Office rule that forces them to work for £1 an hour.
People in immigration detention completed up to 880,000 hours of paid work in 2016-17, with inmates employed as cleaners, interpreters, library assistants, kitchen assistants and barbers, among other roles.
The "vast majority" of the work is paid at £1 per hour, according to Duncan Lewis solicitors, which has issued judicial review proceedings to challenge a Home Office rule, unchanged since 2008, that sets this maximum rate.
In statement seen by Sky News, a detainee claimant working as a cleaner said detainees are the only workers cleaning communal spaces, messy rooms, sinks and toilets in a "disgusting state", in a wing populated by up to 150 people.
They said they feel "taken advantage of".
People in detention might take a job in order to buy essentials such as toiletries, phone credit or additional food stuffs, all of which can be expensive in immigration centres.
N, who wanted to remain anonymous, told Sky News he is earning money to send to his family.
"They have been through hell because of my situation. Whatever I work is for them," he said.
Because of the low pay he can cover little more than basic support for his family and goes without buying extras for himself.
While he enjoys and draws great satisfaction from his work - which he feels is necessary, helps other detainees, and keeps him engaged - he feels the pay he receives should be "commensurate" with what the work is worth.
"It's something I want to make a living from," he said, adding a change would make a big difference to him, and to other detainees, many of whom are saddled with large legal costs.
Claimants are also objecting to a lack of flexibility from the Home Office, which offers no chance of bonuses or overtime increases.
Lawyers say this means immigration detainees have a worse lot than prisoners - who are often paid less but get bonus opportunities.
A Home Office spokesperson told Sky News that paid work opportunities were entirely voluntary for detainees and help "keep them occupied whilst their removal is arranged".
"The numbers of detainees volunteering for paid activities across the detention estate is evidence that the jobs are popular," a spokesperson said. "This practice is not a substitute for the work of trained staff."
However, both detainees and the lawyers representing them say they believe the centres often depend on the work of detainees.
"They're basically cleaning their own detention centre so they can live there. It's framed as giving them a chance, but it's really just exploitative," lawyer Philip Armitage said.