The Supreme Court judgment on the use of tikanga is audacious.
It hijacked the Peter Ellis case to insert the issue of tikanga into it when neither of the parties before it had sought it.
It did so while knowing that upon his death from terminal cancer, it already had ample discretion to progress the Ellis case under its current rules without reference to tikanga.
Worse, it has rewritten the law on tikanga knowing full well that the Government had asked the Law Commission to undertake a detailed study of the role of tikanga in common law.
The court decided to usurp that work and pronounce a significant change to the law about when tikanga should be recognised in common law, while at the same time paying lip service to an evolutionary approach to the development of the common law.
It would have been quite appropriate for the court to have developed new law if it had been essential for the Ellis case, and there was a gap in policy development.
Neither of those is true.
The Government is entitled to grapple with the major issues of the day by identifying issues, getting expert views, formulating policy, introducing legislation, getting feedback from the public and passing laws.
The unelected Supreme Court knew that was happening on the issue of tikanga but ignored it to impose its own views on an issue after contriving to be confronted with it.
It was Justice Susan Glazebrook who first suggested to Peter Ellis' team during a hearing that it might develop arguments about tikanga Māori to support its case, despite him being Pākehā.
He had been already been granted leave to appeal his convictions, but once it was evident he was dying, Ellis asked the court to continue his case after his death.
It granted the continuance but did not give reasons until it published its decisions on Friday when, understandably, most of the coverage concentrated on the substantive decision that the court had overturned his convictions.
Glazebrook led the 3-2 judgments on applying tikanga to the procedural case which allowed the case to continue upon his death.
Not only had she raised it initially at a hearing, the next day the Supreme Court sent a minute to the lawyers directing that their submissions cover whether tikanga might be relevant, which aspects of tikanga, and how it should be taken into account.
The lawyers for both sides decided to hold a wānanga (meeting) with eminent tikanga experts, including Sir Hirini Moko Mead and Sir Pou Temara, to discuss the issues raised in the court's minute.
Oddly, while having sought and heard evidence on the possible relevance of tikanga to the Ellis case, in a majority of the judges' views (Glazebrook, Mark O'Regan and Sir Terence Arnold), tikanga was not a key factor in deciding that the case should proceed.
And even more oddly, given that it wasn't a key factor, a different majority (Glazebrook, Helen Winkelmann and Joe Williams) decided to change the law on tikanga.
So what is the issue and what has it done?
First the basics: Tikanga is a body of evolving Māori customary law and practices, adapted over time by Māori, and includes values, principles and norms which determine appropriate conduct.
Parliament makes statutes - written laws - which are interpreted by the courts. Some laws, but not many other than Treaty settlements, refer to tikanga.
Common law principles are developed by the courts through its case law decisions which can draw on many sources, including statutes, other cases in New Zealand, cases overseas, international conventions, charters - and tikanga.
The extent to which tikanga is recognised in law has varied. Some cases are intrinsically about tikanga, such as the family fight over whether James Takamore should be buried where he had lived, in Christchurch, or in his ancestral home, in Tuhoe country. In others, it might be a smaller consideration.
Until Friday's decision, the courts have applied a test before tikanga was considered part of the common law: it needed to be a general custom of Māori, it could not be contrary to statute law, and it needed to be reasonable.
That test has been used since 1908 but under the changes by a majority, it has now been abandoned and denounced as a "colonial relic".
The court deemed the test inappropriate and belonging to a time when "native" customs were treated with suspicion.
The decision itself means that courts now have the discretion to apply tikanga in any case they see fit, in any way, without any test.
And there can be no expectation that tikanga in common law will be confined to what might be perceived as Māori issues, as the Ellis case showed.
What it really means is anyone's guess because it will be up to what the judges decide in any given context.
But it must mean greater recognition of tikanga in common law - meaning there will be more instances when Māori custom may be given more weight than written laws or existing common law.
The pro-active insertion of tikanga issues by the court appears to have been in response to criticism the Supreme Court received in 2012 over its Takamore decision.
It was criticised then by Māori law specialists for failing to advance the recognition of tikanga in relation to common law.
Glazebrook had been closely involved in the Takamore case at the Court of Appeal and has a clear interest in tikanga.
She may have been waiting for a case to come along to make what may turn out to be landmark changes in tikanga law.
Two of the judges, Justices O'Regan and Arnold (who has since retired), while appreciating the work of the tikanga experts in relation to the Ellis case, did not believe it required a tikanga approach.
They noted the detailed work the Law Commission was already doing: "We think it is better to allow that process to proceed without the intervention of obiter pronouncements from this Court," they said.
"We prefer to allow the law to develop in cases where the consideration and application or incorporation of tikanga in the decision affects the outcome and, preferably, where there has been an adversarial process in relation to those issues."
That is a very polite way of saying their Supreme Court colleagues have inserted their views at the wrong time on a case that is not appropriate, and without sufficient debate.
Many lawyers and academics will be applauding the use of tikanga in the Ellis decision because they want greater recognition of tikanga in the common law.
But law should not be made like this, vicariously through unrelated vehicles, with little idea of the consequences, and in competition with the executive - which is already trying to grapple with tikanga in the law.
This is judicial activism with a capital A.
The courts have played a leading role in Treaty of Waitangi law over many years because, in the absence of clear Government policy, successive Governments allowed it.
But New Zealand is in transition and there is a lot more happening in the legislative space these days with growing reference to tikanga, not to mention co-governance.
Often board appointments require at least a certain number of people to have expertise in tikanga - that is because the law cannot specify a Māori appointee.
But tikanga is now a feature of what might usually seem innocuous laws, such as the reform of the Plant Varieties Act. Any new commercial development of native plants will have to be handled by a Māori plants committee.
In the original legislation, there was no right of appeal to the High Court for a breeder of native plants because Cabinet decided that the courts were not sufficiently skilled to handle an appeal on a tikanga issue.
It was amended in committee to allow appeal rights on native plants - but to the appellate body of the Māori Land Court, not to the High Court, as breeders of roses have on decisions of the general committee.
So the High Court, which for years has adjudicated after hearing expert evidence on a myriad of complex issues, is now deemed too unskilled in tikanga to decide on native plant issues.
The more this becomes a prevailing view, the more likely it is that the structure of the courts will change in the name of tikanga.
Such transitions need to be done with the maximum public debate and buy-in.