LEIGH SALES, PRESENTER: Detention centre whistleblowers are defying the law to speak out about a culture of cover-ups and abuse on Nauru and challenge the evidence given by centre operators before Parliament.

A Senate inquiry into the island is due to report within days.

Tonight, 7.30 can reveal the likely findings of the committee, including a demand for children to be removed from detention.

As Transfield and Wilson Security seek to renew their lucrative contract to run the detention centres, the conduct of their staff is under more scrutiny, not least over a covert operation to spy on an Australian senator and Wilson's attempt to play it down.

This report from Hayden Cooper.

HAYDEN COOPER, REPORTER: Inside the Nauru detention centre in the hours before the riot of July, 2013. This footage is from a camera worn by one of the Wilson security guards.

SECURITY GUARD: We've got the cops at Charlie 2.

SECURITY GUARD II: Yep.

SECURITY GUARD: If they do try to escape, the coppers want your team up there to give them a hand, arrest the f**kers.

SECURITY GUARD II: Sweet as.

SECURITY GUARD: Alright.

HAYDEN COOPER: The guards are preparing to join Nauruan police at the camp's gate in an effort to contain the unrest.

SECURITY GUARD III: So if something happens, all the cops are on standby out at Charlie 2, man. If something happens and they all go out through here, then we go Charlie 2.

SECURITY GUARD IV: Yeah.

SECURITY GUARD III: Take (beep) down. The cops have asked ERT to assist.

SECURITY GUARD IV: So just grab 'em.

SECURITY GUARD III: We assist the cops in any way in as much capacity as - because you become an authorised officer.

SECURITY GUARD IV: Yeah, yeah, as soon as the cop tells you what to do, you can do it.

SECURITY GUARD III: Yeah.

SECURITY GUARD IV: Now I don't understand Nauruan, so I'm just gonna say he told me to do everything.

SECURITY GUARD V: I'm pretty sure he said shoot that guy. I'm fairly confident he gave me that order.

HAYDEN COOPER: This video has come to light because of more and more Australians who are prepared to defy the new Border Force Act and risk two years' jail by revealing what they experienced on Nauru - guards, social workers, doctors.

DAVID ISAACS, PEDIATRICIAN: If I see child abuse in Australia and I don't report it, I can get into enormous trouble. If I see child abuse on Nauru and I do report it, I might go to prison for two years.

NATASHA BLUCHER, SOCIAL WORKER: Australian people deserve to know what's being done in their name with their tax money. And - and they don't know.

HAYDEN COOPER: Tonight, 7.30 reveals a rare glimpse of life on Nauru, through photographs, videos filmed by asylum seekers and the testimony of those who worked there. A former Wilson Security guard who feels compelled to speak out.

Is this sort of abuse still going on, do you think?

FORMER WILSON SECURITY GUARD: I'd say definitely, yes.

HAYDEN COOPER: Paediatrician David Isaacs, a man still shocked by what he witnessed on Naura during a visit last December.

DAVID ISAACS: I saw a six-year-old girl who tried to hang herself with a fence tie and had marks around her neck. I've never seen a child self-harm of that age before.

HAYDEN COOPER: And there with him was Sydney nurse Alanna Maycock.

ALANNA MAYCOCK, NURSE: David and I heard a report from a mother that we'd seen that she'd been raped there. She was offered more time in the showers for sexual favours.

DAVID ISAACS: After five days, I went home and had nightmares. I didn't expect that. I didn't expect to be so, um, traumatised by these people's trauma. These are people, ordinary people and we're treating them with, um - sorry. We're treating them with incredible cruelty.

HAYDEN COOPER: These serious allegations of rape, self-harm and abuse have dominated the Senate inquiry, and since, some have been referred to Nauruan police. But the responses of centre operators Transfield and Wilson Security are now being called into question. Both claim staff are trained to report abuse, including through a special hotline.

NAURU DETENTION CENTRE OPERATOR REPRESENTATIVE: We have had this whistleblower hotline in place for a long time. It is actually on the backdrop of every person's screen at work.

HAYDEN COOPER: This former guard says otherwise.

FORMER WILSON SECURITY GUARD: I'd never heard of it. During my induction course when I first started work, they never mentioned it and the whole time I worked there, I never heard of it.

HAYDEN COOPER: No-one said there's a hotline you can call if you want to report abuse or anything like that?

FORMER WILSON SECURITY GUARD: Never.

HAYDEN COOPER: You never saw the whistleblower hotline advertised?

FORMER WILSON SECURITY GUARD: Never.

HAYDEN COOPER: Alcohol and drug use among guards and other staff on Nauru is a problem. This record of a Wilson Security management meeting obtained by 7.30 confirms the incidents of alcohol abuse.

Transfield told the inquiry that staff on Nauru are subject to random alcohol testing.

SARAH HANSON-YOUNG, GREENS SENATOR: Is it every day?

TRANSFIELD REPRESENTATIVE: Ah - yes, my understanding is every day, testing would occur.

HAYDEN COOPER: Can you describe for me what sort of alcohol testing was done on you while you worked at Nauru?

FORMER WILSON SECURITY GUARD: None, not once. The whole time that I worked there, I was never tested for alcohol and I'd never seen any alcohol testing.

HAYDEN COOPER: You never saw any random breath testing at all?

FORMER WILSON SECURITY GUARD: Not at all.

HAYDEN COOPER: But it's the evidence provided on so-called Operation Raven that several guards now dispute - the spying on Senator Sarah Hanson-Young during her visit to the island, an incident the Government dismissed.

TONY ABBOTT, PRIME MINISTER: I don't accept that characterisation. I believe she was being in fact looked after while she was there.

PETER DUTTON, IMMIGRATION MINISTER: My experience of Sarah Hanson-Young is that she gets most of the facts wrong most of the time.

HAYDEN COOPER: Wilson admitted the spying, but said it was limited in scope to one supervisor and two of his staff.

WILSON SECURITY REPRESENTATIVE: Senator, there was no reporting that came out of this that didn't inform any decision-making. It was the rogue actions of a misaligned individual.

HAYDEN COOPER: But several former guards have told 7.30 that in fact up to eight Wilson employees were involved.

FORMER WILSON SECURITY GUARD: What I was aware of or what I'd heard from other guys who were involved was that they were briefed on her room number, the vehicle and what time she was going to be in and out of the camp. They were also told to follow her and they were told to keep notes on who she was talking to around the island and in her room.

HAYDEN COOPER: So it was quite an extensive spying operation?

FORMER WILSON SECURITY GUARD: Yes.

HAYDEN COOPER: Do you have any doubts about that at all?

FORMER WILSON SECURITY GUARD: I have no doubts.

HAYDEN COOPER: Later when news spread, they panicked.

FORMER WILSON SECURITY GUARD: Basically, the individuals involved and the supervisor were called into the Wilson office. They were told to shred pages from their notebooks and any reports they had written up.

HAYDEN COOPER: It's not yet clear if the committee will refer this allegation to Australian Federal Police.

With the Senate inquiry drawing to a close, 7.30 understands it will make a number of key recommendations. These are likely to include a demand for children to be removed from detention, for the reporting of sexual abuse to be made mandatory and for the Immigration Department and Federal Police to conduct a full audit of all allegations. The committee may also recommend comprehensive drug and alcohol testing on Nauru and for the Immigration Ombudsman to review all complaints made against detention centre staff.

These photos obtained by 7.30 reveal the mouldy and ramshackle tents housing asylum seekers. 700 are held on Nauru at a cost per detainee of $2,000 a day.

Natasha Blucher is another former staffer who won't stay quiet. She worked for Save the Children and wants the centre closed, but she's pragmatic.

NATASHA BLUCHER: You won't get an argument from me in relation to whether or not we need to stop the boats. We shouldn't have people getting on boats because they're desperate and drowning. Like, that argument does have merit. But you can't tell me that in a country that's developed and full of educated people, that we can't do it in a way that's not so brutal and doesn't cause so much harm to people.

HAYDEN COOPER: Dr David Isaacs believes he'll never return to Nauru because he won't be allowed back - the price of ignoring the Border Force Act and going public.

DAVID ISAACS: It's child abuse. Putting children in detention is child abuse. So, our Government is abusing children in our name.

LEIGH SALES: Hayden Cooper reporting.