Two former detainees have taken the Home Office to the High Court over alleged abuse at G4S-run Brook House immigration removal centre.
The Home Office has asked the Prisons and Probation Ombudsman (PPO) to hold an investigation, but the men say human rights laws require a public inquiry.
They argue the PPO probe cannot compel witnesses to give evidence and will only have minimal victim participation.
Staff at the facility near Gatwick were filmed by an undercover BBC reporter.
Panorama footage shown in September 2017 showed alleged assaults, humiliation and verbal abuse of detainees by officers at the centre.
At least six staff members were dismissed by G4S.
The men bringing the case, who are known as MA and BB, are backed by the Equality and Human Rights Commission.
Nick Armstrong, representing BBÂ said further allegations by a number of ex-detainees included deliberate and unjustified use of force by staff, repeated segregation of detainees with serious mental ill-health and endemic drug use facilitated and tolerated by staff.
