Campaigners have criticised private firms for using immigration detainees as cheap labour inside detention centres after research suggested this saves them millions of pounds. Some detainees said they were being paid as little as £1 an hour to cook and clean. Home Office figures showed that in May this year, detainees in centres run by Serco, G4S and other contractors did nearly 45,000 hours of work for a total of nearly £45,500 in pay. Had they been paid at the national minimum wage, the cost would have been more than £280,000. Over 12 months, the figures suggest that the firms – which also include Mitie and GEO – could have saved more than £2.8m, according to research group Corporate Watch, which obtained the data, and said firms were "exploiting their captive migrant workforce"....On behalf of the firms, a Home Office spokesman said: "The long-standing practice of offering paid work to detainees has been praised by Her Majesty's inspectorate of prisons as it helps to keep them occupied whilst their removal is being arranged. Whether or not they wish to participate is entirely up to the detainees themselves. This practice is not intended to substitute the work of trained staff." Wyn Jones, of Serco, said the paid work was voluntary and in accordance with Home Office rules. He added: "It is offered to residents alongside other constructive activities to help reduce boredom and improve mental health and, if not conducted, would have no effect on the running of the [centres]. Serco refutes any implication that we use residents to conduct work in place of officers or staff at any of the IRCs that we manage and thereby increase profits."