Peter Dutton has sweeping and unchecked powers that are beyond the review of courts, are unjust and “un-Australian” and must be wound back, a former immigration minister has said.

The comments, by the former Fraser-era immigration minister Ian Macphee, come in a report that has examined the discretionary powers of immigration ministers and found them to be dramatically increasing, and adversely affecting asylum seekers.

The report by Liberty Victoria’s Rights Advocacy Project, which was released on Thursday, called for current powers to be reined in and for bills to expand them even further to be stopped.

In a foreword to to the report, McPhee said he was “disgusted by the power accorded to current ministers regarding the lives of people fleeing persecution”.

“Ministers now exercise power that is mostly beyond the review of judges,” he said. “Such power should be exercised humanely and in accordance with morality, not absolute law.

“The law and its practice is now unjust. It is un-Australian.”

Current powers include various discretions to approve, refuse, or cancel visas, to detain or re-detain an asylum seeker without warning, to send asylum seekers to offshore detention centres and, in some cases, prevent reviews of decisions not to grant protection visas.

In recent years a number of high-profile asylum seeker cases have made headlines for the minister’s decision to use – or decision not to use – his discretionary powers in their favour.

The report found the creation and use of discretionary powers, particularly under immigration and national security legislation, had risen over decades, despite warnings from several previous ministers.

The report also pointed to two current Coalition bills that seek to expand them even further under the current minister, Dutton. These powers, the RAP said, would further allow an immigration minister to “play god”.

“Those decisions are not made in a transparent way in accordance with fair processes,” the report said.

“Rather, the minister is empowered to an alarming degree to make decisions based upon his whim, with scant regard for due process.”

The report examined the number of acts administered by each minister and the number of “public interest” or “national interest” powers that conferred largely undefined ministerial discretion.

It found the immigration minister’s haul far exceeded cabinet colleagues, with 47 powers within 20 acts. The attorney general held 38 powers – the second highest amount – but those were within 152 administered acts.

“This is an astonishing development of unchecked discretionary power considering that in 1989 there were only three comparable public interest based discretionary powers and, prior to that, there were none whatsoever,” the report said.

Report author Lauren Bull said: “Under Australian law, no other minister – not even the prime minister – is given anywhere near as much unchecked power.

“It is fundamentally at odds with basic principles of democracy and the rule of law for one politician to have [that much] personal power to make such important decisions affecting people’s most basic of rights.”

Among its recommendations, the RAP called for the full restoration of natural justice, which has been specifically written out of some laws including those relating to turnbacks and the provision of natural justice at sea.

“The key takeaway about natural justice is this notion of a fair go,” a co-author of the report, Elizabeth Colliver, told Guardian Australia. “It means a decision which affects someone’s interests, someone’s rights, that they should have the right to appeal and be heard by an impartial decision maker.”

The report also called for the eradication of the controversial ministerial satisfaction test, which allows a minister to decide if he is satisfied certain conditions have been met in order to trigger discretionary powers. The test appears throughout the Migration Act, including in relation to bridging visas and visa cancellations.

McPhee told Guardian Australia he believed the security concerns and protections often cited by recent immigration ministers could still be addressed with greater oversight of their decisions.

McPhee said the Fraser government had aimed to settle refugees in a “welcoming and humane manner”, working with the UNHCR and regional partners, but, since the prime ministership of John Howard, that had reversed.

“It’s just appalling the situation that has arisen,’ he said. “I don’t know how anyone like Morrison or Dutton can be proud of what they’re doing. It’s against the Australian idea of a fair go.”

A 2004 Senate inquiry into the issue found there were serious concerns about vesting “non-delegable, non-reviewable and non-compellable discretion” without adequate oversight. It found a “pressing need for reform” but recommended keeping the ministerial discretion powers as “the ultimate safety net” and a last resort to deal with exceptional or unforeseeable cases.

A 2016 review made similar recommendations.