Scott Morrison's tough new plan to send asylum seekers home if they have a less than 50 per cent chance of torture or persecution defies a longstanding High Court ruling and breaches our international obligations, writes Greg Barns.

As the number of refugees in the world tops 50 million, it is extraordinary that a wealthy democracy like Australia would be making it more difficult for desperate people to come here and seek security.

But that is exactly what Immigration Minister Scott Morrison has done when yesterday when he introduced changes to the Migration Act that seek to overturn almost three decades of legal authority on the assessment of risk of persecution or serious harm if a person is not granted refugee status in Australia.

Under the 1951 Refugee Convention, to which Australia is still a signatory, a refugee is a person who, "owing to well-founded fear of being persecuted for reasons of race, religion, nationality, membership of a particular social group, or political opinion, is outside the country of his nationality ... or country of former habitual residence".

A "well-founded fear" has been interpreted since 1989 in Australia to mean that a person seeking refugee status must show that there is a real chance of their being persecuted if returned to the country in which they previously lived.

In 1989 High Court Chief Justice Anthony Mason, in a decision called Chan, set out what is termed the "real chance" test. He wrote that it:

Clearly conveys the notion of a substantial, as distinct from a remote chance, of persecution occurring ... If an applicant establishes that there is a real chance of persecution, then his fear, assuming that he has such a fear, is well-founded, notwithstanding that there is less than a 50 per cent chance of persecution occurring. This interpretation fulfils the objects of the Convention in securing recognition of refugee status for those persons who have a legitimate or justified fear of persecution on political grounds if they are returned to their country of origin.

The decision in Chan was affirmed in another decision of the High Court called Guo in 1997. This test has been applied consistently in tens of thousands of cases since 1989.

But Minister Morrison wants to undermine Australia's Refugee Convention obligations by replacing the "real chance" test with a new "more likely than not" test, which would mean that an applicant for refugee status in Australia would have to demonstrate a "greater than 50 per cent chance" of them suffering significant harm or persecution if returned to the country they fled.

Extraordinarily Minister Morrison claims that such a test will still enable Australia to meet its international obligations. This is simply wrong.

The "real chance" test or variants of it have been adopted in many countries because it is so patently unfair to read an international law designed to assist desperate people in a restrictive way that undermines the intent of the law. The US, New Zealand and Canada are all examples of jurisdictions that do not insist on a 50 per cent or better type test.

The test Mr Morrison proposes is essentially a balance of probabilities type test.

In other words, an asylum seeker would have to prove it more probable than not that persecution or serious harm would happen to them if Australia refused them a visa.

Such a proposition is antithetical to the Refugee Convention because it wrongly applies a principle of law that is suited to cases where it is events in the past that are being examined.

In a civil action where a person is, for example, suing the Commonwealth government for mental and physical harm that is alleged to be caused by their detention on Manus Island, what a court is examining is events in the past - the period the person was in the centre.

A court can decide that it is more likely than not that the Commonwealth caused harm to that person or did not, as the case may be, by reference to what has happened. But in the case of an applicant for refugee status the court or decision maker is being asked to look into future - what would happen if that person were sent back to the country where they lived?

When assessing the future, unless one has a crystal ball or some mystical power, then it is intellectually untenable to make prognostications that persecution is more likely than not to occur. The nature of the future, particularly in unstable parts of the world, makes decisions about what might happen to a person more difficult.

It is right to err on the side of caution because what is at stake is a human life and the responsibility of a country like Australia to not send individuals back to situations where they are tortured or killed.

Minister Morrison's changes, if they pass the Senate, would inevitably mean an increase in the number of people shunted back to situations where their lives would be at grave risk.

This is cruel and it certainly is not consistent with the obligation this country has under the Refugee Convention.

Greg Barns is a barrister and a spokesman for the Australian Lawyers Alliance. View his full profile here.