In 2011, the Commonwealth passed legislation making it a crime for recipients of social security to fail to report changes to their financial circumstances to Centrelink (our social security agency) within 14 days (Social Security and Other Legislation (Miscellaneous Measures) Act 2011(Cth) ). This legislation was made retrospective back to 2000.

This law was challenged the other day in the High Court, and it was ruled that this obligation did not apply retrospectively. Relevant news article: http://www.abc.net.au/news/2013-05-08/high-court-to-consider-welfare-fraud-laws/4676454.

This got me thinking, are retrospective laws constitutional in general in Australia? To compare opposite sides of the spectrum, the US constitution states that "No Bill of Attainder or ex post facto Law shall be passed", whilst in the UK, parliament has the power to do pretty much whatever it wants. Australia's political system is similar to that of the UK, but we have a formal constitution like the US that describes the powers of government.

As far as I'm aware, our constitution contains no specific prohibition of such. Why then did the High Court determine it had the power to strike the retrospective part of the act? I'm no legal expert, but despite the reporting in the media, it seems to me that the High Court did not actually address the question of retrospectivity. In their judgement (http://www.austlii.edu.au/au/cases/cth/HCA/2013/20.html) they say that the law does not "create a duty" to disclose these changes in circumstance effective 2000, and then apparently decline to address "is section 66A of the Administration Act invalid, insofar as it has retrospective effect, because it infringes the separation of judicial and legislative powers mandated by the Constitution? "

So, the question: what are the limitations, if any, on retrospective laws in Australia?

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    Good question, but needs to be answered in a manner that cannot be construed as legal advice. Commented May 9, 2013 at 4:33
  • Don't worry, I'm not being chased for welfare fraud because of this! Commented May 9, 2013 at 4:47
  • Don't kid yourself, the US constitution doesn't protect us from retroactive tax laws. US v Carlton showed that if the government (1) the legislation has a rational legislative purpose and is not arbitrary; and (2) the period of retroactivity is not excessive that they could still get your money. Congress never thinks taxes are arbitrary, and they also don't think the length of copyright is excessive...good luck if you "owe" the IRS retro
    – user1873
    Commented May 9, 2013 at 13:48
  • Useful hint - these are called ex post facto laws... Although with taxes, there are special loopholes Commented May 9, 2013 at 16:16
  • Ok, nothing to do with Australia, but for example in Hungary in 2011 they taxed 98% on certain government gaven premiums and final honoraries retrospectively between 2002-2010 which era ruled by different party. Commented May 13, 2013 at 8:11

2 Answers 2


All right, I'll bite: see Retrospective laws breach separation of powers.


A bill of attainder is an obvious breach of the separation of powers. A retrospective law creating criminal liability is tantamount to a bill of attainder.

Furthermore, because a judicial finding of law is retrospective to the last relevant legislative change, a legislative change cannot be retrospective without usurping a judicial function.

Even without an explicit separation of powers, the mere existence of a constitution, or of a court, recognizes the rule of law, which in turn gives an implicit separation of powers.

The rule of law has three further implications which exclude retrospective laws creating criminal liability. First, the law must be knowable. If a retrospective law is to satisfy this requirement, it must be so obvious that it is knowable before it is enacted. Second, the law cannot demand the impossible. Hence it cannot require us to know a law that has not yet been made and is not knowable until it is made. Third, we are under a "government of laws", but a general power to make retrospective laws would place us under a "government of men".

It is arguable that a retrospective law is permitted if it only produces an otherwise permitted effect. At a stretch, that argument would permit a retrospective law criminalizing activities that were already crimes under non-retrospective laws (though one might ask what is the point). But it does not support retrospective legislation criminalizing activities that would not otherwise have been crimes at all.

(e.g. IANAL; TINLA, etc.)

P.S.: Response to Samuel Russell's comment

Samuel Russell writes: "Putland's analysis in that blog post relies on the US constitution to make an argument in relation to Australia..."

Not quite. My discussion of the U.S. Constitution in the blog post concludes that "bills of attainder and ex post facto laws..., if they were not explicitly forbidden by particular clauses of the U.S. Constitution, would be implicitly forbidden by the separation of powers." And of course Australia has the separation of powers. Hence I didn't find it necessary to mention the U.S. constitution in the above summary.

While opinion varies on how much is implied by the rule of law, the minimalist opinion is that the law must be knowable and therefore prospective. If that's all it takes to be "tendential", so be it. My contention that the rule of law and its implications are already binding, and not merely aspirational, is more original; but Russell doesn't argue with that.

He does argue against my claim that the rule of law implies the separation of powers. But the rejection of ex post facto laws survives without that claim; it follows from the rule of law, and it follows from the separation of powers, regardless of any connection between the two.

Concerning the UK, I admit that the separation of the Supreme Court from the House of Lords was centuries overdue. The former arrangement did not give a structural separation of powers. Whether it gave enough functional separation to satisfy the rule of law depends on the effectiveness of mechanisms for avoiding conflicts of interest (on which I'm not in a position to comment further). Note that my derivation of the separation of powers from the rule of law does not specify the extent to which the executive branch is answerable to, or drawn from, the legislative branch; thus it neither endorses nor rejects the Westminster system per se, although it does warn against tight party discipline that results in a domination of Parliament by the Executive.

Concerning the history of the separation of powers in Australia, I am aware that the High Court has taken a narrow view of what tribunals can exercise judicial power. But I would have thought that strengthens the case against usurpation of judicial power by the legislature.

  • I've added a summary as suggested. Commented May 15, 2013 at 11:29
  • Thanks a bunch, that's an amazing answer! So basically, if I've understood right, the government messed up the legislation so the high court did not interpret it as retrospective, but if they fix it it'll be invalid on the grounds that it usurps judicial power contrary to section 3 of the constitution, right? Commented May 15, 2013 at 13:01
  • In my amateur but vehement opinion, yes - except that you mean chapter 3 of the Constitution. Commented May 15, 2013 at 13:26
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    Putland's analysis in that blog post relies on the US constitution to make an argument in relation to Australia, and tendentially construes the rule of law. The United Kingdom manages without a separation of powers, and manages to maintain a rule of law. Putland's argument falls on this point. Putland could improve his argument, and thereby this answer could be improved, with reference to cases where the separation of powers was established in Australian law (Arbitration Court's case for example?) rather than as a universal principle inherent in government. Commented May 15, 2013 at 22:58
  • Maybe not entirely on topic but I feel that the US perspective that the US constitution is somehow superior to those of other developed nations ignores the factual evidence on the ground. A written constitution and a strict separation of powers has not exactly saved the US from committing great sins domestically.
    – Simd
    Commented May 5, 2015 at 6:23

The separation of powers applies only to the Aus federal govt, and not to the states. About the only restriction on the states is Sec 3, which bans bills of penalties. The HC (13/2015) has now ruled that a bill of penalties must at least name the individuals involved. (An easy restriction to side step.) The states may pass any type of legislation that is not contravened by federal legislation. For example, a state may pass a law fining all Jews as a punishment for killing Jesus. That is 100% constitutional.

The ICAC hearings are tantamount to kangaroo courts, and penalties are imposed directly by state legislation. All perfectly constitutional.

The UK government is subject the bill of 1689, which bans bills of attainder and penalties.

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