Some of the 267 asylum seekers waiting to be flown back to Nauru are suffering from cancer and terminal illnesses, and the first returns could potentially be made “within days”, Immigration Department chief Michael Pezzullo says.

In a Senate estimates hearing on Monday, department officials also denied that one of the people awaiting return was a 5-year-old child that had been raped, saying the child involved in the incident was more than twice that age and suffered only “skin to skin contact” with another detainee child.

The Turnbull government is under intense pressure to allow the group, including 37 babies, to remain in Australia.

In explosive revelations to hearing, the government’s top medical adviser on immigration detention, John Brayley, admitted keeping children behind wire has a “deleterious” effect on their mental health and “wherever possible children should not be in detention”.

Mr Pezzullo told the senators his department would take advice from doctors over when to return the group, which largely comprises those who came to Australia for medical treatment and their families. They included people with Illnesses such as cancer, and some conditions that were “terminal”.

“Depending on how their care is going … we will work through those in a staged fashion,” he said, adding decisions would not be made in a “bulk determination”.

Medical advice indicated some people would require more than six months treatment while others would be fit to travel “soon …  it’s possible that some people are ready to go within days”.

A High Court ruling last week that found the offshore detention regime was legal meant the department was “on very clear legal footing” that returns could take place, but saying “you all have to leave in one planeload” was not appropriate or sensible, he said. 

Mr Pezzullo said as medical facilities at Nauru improved “there will be less and less requirement to repatriate people to Australia” for treatment.

Children in detention has ‘deleterious’ effect

In the hearing, the department’s chief medical officer Dr Brayley, admitted keeping children behind wire has a “deleterious” effect on their mental health, and revealed the parents of most children detained in Australia and Nauru have reported their children display abnormal behaviour.

“The scientific evidence is that detention affects the mental state of children. It’s deleterious and wherever possible children should not be in detention,” he said.

Dr Brayley said this effect had been measured in a number of ways, including by tools used by the Australian Human Rights Commission, which he described as “robust”.

As Fairfax Media reported last week, the commission found that 95 per cent of asylum-seeker children who had lived at Nauru are at risk of developing post-traumatic stress disorder,

Dr Brayley said the department uses a “strengths and difficulties” questionnaire commonly used in mental health in Australia.

It involved 25 items covering emotional symptoms, conduct problems, hyperactivity and inattention, peer relationship problems and pro-social behaviours.

Parents complete the questionnaire for children aged under 11, while older children respond themselves.

Dr Brayley said the parents of 45 children in offshore detention completed the assessment, and 67 per cent scored their child in the abnormal category.

Of 18 children aged 11 to 17 years who self-reported, 33 per cent scored themselves as abnormal and 22 per cent were in the borderline category.

Explaining the discrepancy, Dr Brayley said parents will often recognise problems in their children that children themselves cannot identify.

At Nauru 71 per cent of parents scored their child as abnormal, and 16 per cent of older children scored themselves as abnormal. Some 25 per cent categorised themselves as borderline.

He added that the government was trying to remove children from detention.

Mr Pezzullo said the question of keeping children in detention “is a factual matter that has to be determined in each case”.

He said a blanket policy that no child could be kept in detention “opens the door for many more to arrive”.

Cabinet leak referred to police

Meantime, it emerged that immigration officials have called in the Australian Federal Police over an internal leaked document that suggested Australia’s humanitarian program could face much greater scrutiny and be denied direct access to permanent residency.

As reported by the ABC and Fairfax Media last week, a sensitive draft cabinet document revealed a raft of dramatic measures being considered by the Turnbull government, including subjecting the 12,000 refugees to be taken from Syria and Iraq to more stringent character, identity and security checks than European countries and changing the make-up of the intake to minimise the risk of “extremist infiltration”.

The document, prepared by Immigration Minister Peter Dutton’s department, said the minister will bring forward the proposals in the first half of this year to “mitigate radicalisation risks” of new humanitarian arrivals. 

Mr Pezzullo confirmed the leak had been referred to the AFP as “potential criminal breach”, that could result in a jail term.

He said the document “was internal to the bureaucracy, it had not been sent to ministers and their staff” including Prime Minister Malcolm Turnbull.

Following the leak, a spokesperson for Mr Dutton would not say if he supported the proposals, telling Fairfax Media “this is a draft document which has not been seen by the minister or his staff – nothing more.”

On Monday Mr Pezzullo said said he “can’t rule out … discussions over the telephone or other oral discussions” between departmental officers and the minister’s office over the document.

Asked if his staff engaged with the minister’ office he said “I certainly couldn’t rule that out”.

Department official Rachel Noble said her staff had conversations with the minister’s advisers over the “process” for the preparation of the document, including when it should be prepared.

Child rape claim denied

Mr Pezzullo also denied reports that first emerged on the ABC, alleging that a five-year-old child who had been raped at Nauru was among those awaiting return.

“There is no five-year-old child – it’s a figment,” he said, adding the pediatrician who took part in the broadcast, Karen Zwi, “has conveyed to the department she doesn’t understand how the reference to a five-year-old child emerged”.

He said some media reporting of the asylum seeker issue was “advocacy parading as journalism” and “pamphleteering of an almost political nature” which bent the facts.

Department official Cheryl-anne Moy said the incident involved “physical skin-to-skin contact” and the child was “more than double the age of five”.

She said the attacker was another child transferee. The allegations were raised by the child’s parent, the family was supported with medical, welfare and counselling assistance and the child was moved to Australia for treatment. The boy is living in the community with family in NSW, she said.

People smuggling cost falls

Australian Border Force commissioner Roman Quaedvlieg also revealed the price of a people smuggling voyage from Indonesia to Australia has dropped to about $US $2000, down from about $US10,000 in mid-2013.

He said since Operation Sovereign Borders began cracking down on the illegal trade “that price has dropped significantly” and people smugglers were “struggling to find … customers”.

The hearing continues.