The entire police force has in effect been trespassed from a Wellington property to stop officers checking whether a heavy-sleeping offender is complying with an overnight bail curfew.

In what may be the first case of its kind, police have been left powerless to act after lawyer Douglas Ewen used a centuries-old right to stop the unwanted visits to the Miramar house.

Mr Ewen wrote to Police Commissioner Peter Marshall last week on behalf of the occupants of the property to which Aubrey Renata Haerewa Toheriri, 23, has been curfewed between 10pm and 10am as a condition of his bail on charges of assault and theft. Toheriri is due back in court on Monday for sentencing.

The letter to police revoked the "implied licence" for all police employees to enter the property.

Once the implied licence is revoked, police would be trespassing if they go to the house unless they have a search warrant or other legal authority.

Police say they are assessing the implications of the letter and how to respond.

But Greg O'Connor, president of police union the Police Association, says the law may have to be changed, or police may have to ask for defendants to promise not to revoke the implied licence if bail terms include a curfew. In serious cases, a defendant could be remanded in custody.

Curfews were generally imposed because offences were committed at night and the bail checks were a significant factor in reducing crime, Mr O'Connor said.

"If people would stop offending at 4am then police would stop checking at that time."

The "reverse curfew" imposed on Toheriri in lieu of curfew checks is that he must not be found away from the house from 8pm to 7am. Mr O'Connor said that was a much less meaningful bail condition.

Toheriri's mother said she, her son, and a 14-year-old grandchild had endured two or three months of police checking the curfew about three nights a week, sometimes more than once a night. After nights of broken sleep, the 14-year-old still had to get up for school and she had to go to work.

Toheriri was a heavy sleeper and sometimes someone would have to wake him when police came to the house, she said.

"He got himself into that predicament, but it was unsettling for everyone."

The police checks became too disruptive and they accepted the course Mr Ewen suggested.

In Wellington District Court on Tuesday, police prosecutor Blake Dawson said revoking the implied licence made a mockery of the bail conditions.

He asked for bail to be changed so Toheriri had to live somewhere where the curfew condition could be checked, or for him to be remanded in custody, but Judge Mike Behrens, QC, imposed the "reverse curfew".

Police said that was a problem because they could do nothing if Toheriri left the house but could not be found.

Law Society criminal law committee convener Jonathan Krebs said revoking the police's implied licence to go on to a property was not a course of action he would advise. Being freed on bail was not necessarily a right and could result in the client being remanded in custody instead.

Wellington civil liberties lawyer Michael Bott said he knew of cases in which police were "overly assiduous" in checking curfews so that it became a "tool of oppression". "It is hugely exhausting if it goes on for long periods."

Police were sometimes prepared to negotiate the way a curfew was checked but that was not always possible.

AN ANCIENT RIGHT

"Implied licence" to enter private property has been recognised for centuries to allow citizens to go on to someone's property and knock on the door to make an inquiry.

An occupier can revoke the licence at will by giving notice to the person or people intended to be excluded. Entry after the licence has been revoked would amount to trespass.

However, revoking the implied licence would not stop police going to the house under the authority of a search warrant, or under powers given in statutes such as the Misuse of Drugs Act, the Crimes Act, and the Animal Welfare Act.