20/02/2017 10:32 AM AEDT | Updated 20/02/2017 1:37 PM AEDT

1900 Manus Asylum Seekers In Massive Class Action Against The Government

It's said to be largest immigration detention trial in history.

Law firm Slater and Gordon is gearing up for an historic class action case, taking the federal government to court on behalf of 1900 asylum seekers detained on Manus Island.

Slater and Gordon says its case will be "the largest trial concerning immigration detention in Australian legal history", pursuing the government for compensation for the men over physical and psychological injuries as well as false imprisonment as part of Australia's hardline immigration detention policy.

The lead plaintiff on the case is an Iranian man who spent several years at the Manus facility, in Papua New Guinea, but includes 1905 men who have been detained on Manus since 2012. On Monday, the law firm released details around the case, due to begin in May, which it says will be the first of its kind to be heard in an Australian court.

"This is one of the most factually and logistically complex class actions in recent times," said Slater and Gordon practice group leader Rory Walsh.

"It has been building for two and a half years now and will go to trial after the six parties have considered more than 200,000 discovered documents, 104 witness outlines and 17 expert reports. This case will be the largest and most forensic public examination of the events and conditions at the Manus Island centre and reflects the unquestionable importance of access to justice in the Australian legal system."

Pacific Press via Getty Images
Protests against immigration detention on Manus Island and Nauru have taken place for years in Australia

Slater and Gordon said they were challenging the Commonwealth government, security contractor G4S and service provider Broadspectrum, as well as "two third parties" in medical services provider International Health & Medical Services and security provider Wilson Security. The case commenced in December 2014, with the law firm pursuing compensation for injuries, with a false imprisonment claim added last year after the Papua New Guinea Supreme Court ruled that detention on Manus was in breach of the country's constitution.

"One of the central disputes of this action is whether the Commonwealth is in effective control of the Manus Island detention centre and therefore owes a duty of care to protect the people being held there from foreseeable harm," Walsh said.

"This case addresses systemic issues that have been affecting detainees in relation to the provision of medical services, shelter and accommodation, food, water and security. The action will also determine whether the detention of asylum seekers at the centre amounted to false imprisonment, following the PNG Supreme Court's decision last year that the operation of the centre was not permitted under the country's Constitution."

Stringer . / Reuters

The case is due to start on May 1, and run for three to six months. The case will initially determine whether the detainees have a claim to compensation and, if so, the specific amount of compensation will be determined at a later date. Walsh said the case would help shed light on Australia's secretive immigration detention regime.

"The extraordinary secrecy surrounding the Manus Island detention centre has meant that, for too long, the detainees' experiences have been a case of 'out of sight, out of mind'," he said.

"The remote location of the centre, the difficulties involved in media access and extensive restrictions on workers speaking out publicly have all significantly complicated the legal journey. The group members in this case have had to endure an extremely difficult burden for an extraordinary length of time but we are confident that, come May 2017, their stories will be heard in way that, so far, has not been possible."