Gang patches and other insignia will be banned in Wanganui after a law giving police the power to arrest, seize and fine wearers was passed in Parliament last night.

The measure is a New Zealand first, and other areas with gang problems were last night considering seeking their own versions of it.

Wanganui Mayor Michael Laws said banning patches "removes gangs' most powerful and intimidatory weapon".

He said New Zealanders viewed gangs as a criminal menace and home-grown terrorists.

"It took Wanganui to say 'no more' first."

Mr Laws said the law would have flow-on effects, as other mayors were waiting for Wanganui's lead.

It set a precedent in anti-gang measures, like the recent outlawing of gangs in South Australia.

The law gives the Wanganui District Council the power to make by-laws banning Black Power, the Mongrel Mob, Hell's Angels and other gangs from designated places such as the central business district and parks.

Mr Laws said signs designating gang-free zones could be up by July once the law was signed by the Governor-General and the first bylaws were passed.

Whanganui MP Chester Borrows said the law would have a major impact on gangs because of their code that they did not lose their patches under any circumstance.

"They'll be hung by their own code."

But gang expert Cam Stokes, who was Auckland's top gang detective, said the ban was "cosmetic" and gangs could get around it by wearing their patch jackets inside out.

Mr Stokes said it would not make any difference to the gang problem.

Wanganui has been beset by gang problems, including the 2007 killing of toddler Jhia Te Tua, who was shot during a gang dispute.

Mr Laws started working towards the ban in 2006 because of gang intimidation in the town centre.

It was originally intended as a by-law, but Bill of Rights issues required it to be approved by Parliament.

The bill was drafted by the council and backed by two-thirds of the 17,000 people who voted in a council referendum.

It was introduced to Parliament as a local bill, promoted by Mr Borrows.

It passed last night only after three Act MPs, including leader Rodney Hide, reversed their earlier opposition.

During the bill's first reading, Mr Hide called it "rubbish", saying he could never support it because it would breach people's fundamental right to wear what they wanted.

Last night, he said he changed his mind after Act MP David Garrett visited Wanganui this week and was assured by local police that it would be enforced and have an effect.

The votes of Mr Hide and Act conservatives Mr Garrett and John Boscawen enabled the Wanganui District Council (Prohibition of Gang Insignia) Bill to pass by 62 votes to 59.

Act's new procedure of letting its MPs vote according to their consciences on all legislation allowed the MPs on its liberal wing, Heather Roy and Sir Roger Douglas, to vote against the bill.

Labour, the Greens and the Maori Party were all against it.

Helen Clark's resignation meant there were only 121 votes in Parliament. The 122nd vote will not return until the by-election in her Mt Albert electorate.

Labour attributed Mr Hide's about-face to a deal with National over Act's "three strikes" bill.

Mayors in Whangarei and Hastings have expressed interest in a similar ban, and provincial areas including Timaru, Nelson and the Bay of Plenty are also interested.

Councils wanting similar bans will have to introduce their own local bills unless the Government introduces a national measure.

Police Association president Greg O'Connor welcomed the legislation, saying it would provide a "proving ground" for nationwide action.

* What it means

Gang patches, regalia, signs or symbols cannot be worn in public in Wanganui.

Police can arrest and seize regalia, using force if necessary.

Police destroy regalia.

Wearers can be fined up to $2000.

* How they voted
For: 62 votes
National 58
United Future 1
Act's Rodney Hide, John Boscawen, David Garrett 3

Against: 59
Labour 42
(the party is one vote down until the Mt Albert byelection)
Progressives 1
Greens 9
Maori 5
Act's Heather Roy and Roger Douglas 2

Gang patch ban passed with a three vote majority. There were 121 votes cast