Act Party leader Don Brash wants the personal use of marijuana decriminalised.

Brash this afternoon gave a speech on law and order to supporters at Waipuna Lodge in Auckland, as his party continues to grapple with internal ructions.

"I have to say, after long and painstaking reflection, I have come to have serious questions about our current marijuana laws," Brash said.

"Apparently, a majority of New Zealanders think this law is an ass."

Brash said he was "haunted" by the thought that a lot of police time and resources could be better deployed by keeping people safe from "real criminals intent on harming us".

An estimated 400,000 New Zealanders regularly used cannabis and harmed no one except, arguably, themselves, which was their prerogative in a free society, he said.

"The police and the courts spend some $100 million of taxpayer money a year enforcing this prohibition of a drug believed by many people to be less dangerous than tobacco or alcohol. Is there really any point to this?" Brash said.

"I hasten to add I do not advocate or approve of marijuana use. Unlike Helen Clark and Peter Dunne, I haven't ever tried it and I have absolutely no intention of doing so. But I have to ask myself by what right I would ban someone else from using it, or support a law that does so, especially when I'm leader of the political party in New Zealand that is most committed to personal freedom."

Brash's call may be considered by some to look a touch desperate.

Since he took over as leader from Rodney Hide, the party's polling has barely shifted and remains at about 2 per cent or less.

The party was struck another blow last night when Parliamentary leader John Boscawen announced he would quit politics at the election. Boscawen, who just weeks earlier was named at number two on the party list, cited family reasons for his change of heart.

Brash expressed regret at Boscawen's departure but insisted the party still had its strongest ever list line-up going in to the November election.

In his speech this afternoon, he said the party's policy on law and order was still a work in progress and he was only outlining "the kind of thinking" that would shape it.

"I'm not saying it's now ACT policy to decriminalise or legalise marijuana. I'm simply saying it's my personal view that we should give the idea serious consideration as there are some strong arguments in its favour - arguments supported by some seriously sober and responsible national and international leaders," he said.

Under former Prime Minister Sir Geoffrey Palmer - "hardly a dope-addled hippy or wild-eyed radical" - the Law Commission had in April recommended allowing cannabis for medicinal use and substituting a cautioning regime for criminal penalties in non-medicinal cases, he said.

Brash also outlined a push for the right to self-defence to be enshrined in the Bill of Rights and for more work on victims rights.