The Greens are going to be a refreshingly unconventional force in the new Parliament, but there is one convention they ought to observe: those who make the laws should not break them - any of them. One of their newly elected list, Nandor Tanczos, says he smokes cannabis and has every intention to continue when he becomes a sworn legislator next week. He holds that he is not breaking the law because, as a Rastafarian, he believes he has a religious dispensation under the Bill of Rights Act. The courts will wrestle with that one if he is not careful. The views of his party leaders are of more concern.

"Good on him," says Rod Donald. "The law is an ass and the sooner we change it the better." Jeanette Fitzsimons says: "I don't have a problem with the occasional breaking of this particular law." We could expect better from those with a term in the legislature behind them. All acts of Parliament depend for their effect on public respect for the law.

The physical enforcing of law would be well nigh impossible if the vast majority had to be coerced to observe it. Police are especially conscious of that. Their job is made more difficult when prominent people preach disregard for any part of the criminal code. Police could be excused if they went to particular efforts to demonstrate that such people cannot commit crime with impunity.

Other difficulties await legislators who advocate selective respect of laws. What will Mr Donald say now to those who want to ignore the Resource Management Act? There are many who consider that law an ass. Almost everybody could name a rule they find pointless or excessive. When Parliament is persuaded to the same view, the law can be changed. But it is tempting fate to decide, as Ms Fitzsimons does, that the use of cannabis can be excused because the new Parliament is likely to decriminalise it.

Parliament is a long way from doing so. True, a select committee last year recommended a review of the drug's legal status after an inquiry into its effects on mental health. A succession of drug researchers, though not all, told the committee that cannabis did not significantly damage the health of smokers and argued that its legal prohibition made its health consequences worse. The police, conceding that their efforts had not reduced the incidence of cannabis use, told the committee they were "open-minded" on decriminalisation. That should not be seen as endorsement: police are frustrated at their inability to control the drug.

But the committee would not go as far as endorsing decriminalisation and nor, surely, will the incoming Parliament without a much wider debate than was held among professionals last year. It is significant that the Labour Party is committed only to a review of the law and if ever the issue came before Parliament it is likely that Labour would give its members a free vote. It is particularly hard to see a Prime Minister who has waged war on tobacco lend her encouragement to another substance for smoking.

The public was firmly opposed to legalising the drug when a Herald-DigiPoll survey asked the question a year ago, and it is doubtful that "decriminalisation" (instant fines instead of court proceedings and convictions) would find much favour. Even the Greens were wary of public opinion on the subject during the election campaign. The country needs a full debate before anything is done.

Campaigners have work to do before they can be confident of changing the law and, in the meantime, if they are legislators, they have a special responsibility to honour it.