The 41-year-old law which governs what people can do on land owned or controlled by others doesn't distinguish between private and public land, an expert in public law says. 

But the courts of New Zealand have applied a "judicial gloss" over the Trespass Act, which means people can only be trespassed from public land - such as Parliament, where protesters have camped out for 10 days over Covid-19 vaccination mandates - if it's considered "reasonable" to do so, University of Otago law professor Andrew Geddis said. 

When it came to private land, the act was simple. 

"A private landowner can trespass someone for any reason. But with public land the courts have said trespass notices can only be given if it's reasonable to do, and in the case of protests the reasonableness has to be judged on whether it's a justifiable limit on people's right to protest." 

Hundreds of anti-mandate protesters arrived at Parliament after a two-day cross-country convoy 10 days ago, and have refused to leave. Numbers on-site have fluctuated since but were growing today. 

They were trespassed the following day, after setting up camp on Parliament's lawn, and more than 120 people were arrested after attempting to breach police lines. 

The "judicial gloss" over the Trespass Act came from a 1999 High Court appeal ruling in favour of 75 university students charged with trespass during a protest outside Parliament two years earlier. 

The charges against the students were dropped after the court found the decision to trespass them was unreasonable, Geddis said. 

"In the process of deciding it was unreasonable, the court set out a series of things to take into account, such as how long the protest had been going for and how disruptive was it. 

"And basically the student protest had only lasted for a couple of hours and there was no indication it was going to turn violent so the court said that protest ought to have been allowed to carry on a bit Three-hundred tertiary students marched from Victoria University to Parliament's grounds in September 1997 to protest possible changes to tertiary education funding or structures. 

Assembling behind crowd-control barriers erected in anticipation of their arrival the group protested loudly, but peacefully, according to the High Court judgment. 

After being told then Minister of Education Wyatt Creech wouldn't address them, the protest leader told students to take "one small peaceful step forward" for every minute the minister didn't appear. 

"After the protesters had been in Parliament grounds for approximately 60 minutes a member of the staff of the Speaker who had been delegated the task of overseeing protests in the grounds, considered it was appropriate for the protest to end." 

The arrests took place after protesters were told five times they'd be treated as trespassers if they didn't leave Parliament grounds. 

The incident prompted the Speaker to create rules about protests on Parliament grounds, Geddis said. 

"Now the question is, [if] you breach those rules of protest whether that automatically makes your protest unreasonable, or whether even if those rules are breached there still has to be an assessment of whether it'd be reasonable to close this protest down in terms of the rights of protesters." 

The actions of the anti-mandate protesters - in staying overnight, setting up tents and monopolising a public space "probably tips it over" from being an acceptable use of people's rights to vent their frustrations, to one where it was reasonable for the Speaker to trespass protesters, he said. 

"The problem is they arrested 120-odd people … and the protest still carried on. So it's more a question of the ability of the police to enforce the law, rather than whether the law allows for action to be taken." 

The major iwi in Wellington, Te Ātiawa and Ngāti Toa, have also said they don't support the protest. 

While iwi were recognised as having cultural connections to Parliament grounds, the Speaker was the legal occupier, Geddis said. 

But iwi disagreeing with the actions of the protesters might add to the "overall reasonableness" of the Speaker to trespass protesters, he said. 

"Within the legal system generally tikanga is now recognised as being a force of law in the same way as the courts recognise the old Common Law of England as being part of our law. 

"The courts have increasingly started to say tikanga is now a part of the laws of New Zealand and should be applied where relevant."