Former detainees at an immigration removal centre must be given a chance to confront their alleged abusers at an inquiry, a High Court judge has ruled.
The probe is due to investigate claims of "systemic and institutional failures" at Brook House in Surrey.
Two ex-detainees had argued that staff at the G4S-run site would not voluntarily appear at public hearings.
Mrs Justice May agreed, and said the inquiry must "have a power to compel witness attendance".
The probe into alleged institutional failures was set up after BBC Panorama found evidence of abuse at the centre.
At least six members of staff have since been dismissed by G4S.
The judge said that "the egregious nature of the breaches" required the inquiry to be granted additional powers.
She described the accusations as "repeated events, in front of others, where the perpetrators were managers and trainers, as well as ordinary officers".
Mrs Justice May also ruled that the former detainees - named as MA and BB - were entitled to publicly-funded lawyers, saying: "When dignity and humanity has been stripped, one purpose of an effective investigation must be to restore what has been taken away through identifying and confronting those responsible, so far as it is possible.
"How is that to be done in any meaningful way here unless MA and BB, non-lawyers where English is not their first language, are enabled through representation to meet their [alleged] abusers on equal terms?"
In a statement after the hearing, BB said the case had forced him to "relive some of the most painful times in my life," adding that the outcome was a "huge relief".
"I was worried that the voices of the victims would never be heard. I was worried the truth would never come out," he said.
His solicitor Joanna Thomson said the judgement "should now lead to an investigation that will uncover the truth so that there are no further abuse scandals in the UK's immigration removal centres".
MA's solicitor, Lewis Kett, said: "We strongly welcome the judge's findings that further powers are needed. If the Home Office are truly interested in learning lessons from this inquiry, they should welcome it too."
A Home Office spokesman said: "We will consider this ruling carefully. It would be inappropriate to comment further while legal proceedings are ongoing."