A man has had his drink driving charge overturned after the police repeatedly refused to let him go to the toilet and he soiled himself.

The man was fined $800 in the District Court in December but has since appealed his case to the High Court.

In the decision released today from the High Court in Rotorua, Justice Aisla Duffy said the man had been on his way to collect his daughter from a party in May 2017 when he arrived at a police alcohol checkpoint.

He was asked to accompany a constable to a 'booze bus' after breathing above the legal limit of 400 micrograms of alcohol per litre of breath.

It was then that he told police for the first time that he needed to go to the bathroom.

The man spent an hour and 45 minutes in custody undergoing an evidential breath test and a blood test.

"Throughout the time the appellant was in the 'booze bus' awaiting the blood test procedure he repeatedly asked Constable Collingwood for access to a bathroom. No access was provided."

He was unable to maintain control and defecated in his trousers.

Justice Duffy described it as a "humiliating act".

"The nurse responsible for administering the blood test procedure then arrived and the appellant apologised to her for the unpleasant smell. He explained to her why he could not sit down as requested."

After the testing was completed, the constable offered no assistance for the man to clean himself and he was left to walk to a nearby service station to do so before walking home.

Justice Duffy said his treatment breached the New Zealand Bill of Rights Act and went against an detained person's right to be treated with humanity and respect to dignity.

"Once the constable was aware the appellant had soiled himself the constable should have taken steps to give the appellant the opportunity to clean himself.

Justice Duffy said he should have been offered facilities at the police station which was about 1.2km away.

"This careless impropriety was entirely unnecessary. There was nothing to stop the constable from allowing the appellant access to bathroom facility.

"I also find it of concern that the respondent was prepared to argue, up to the time of the appeal hearing, that an adult male in the appellant's circumstances should have been able to exercise sufficient self-control to avoid soiling himself.

"This suggests to me that the respondent has failed to recognise the enormity of what has occurred here."

Justice Duffy set aside the man's conviction.

'Outraged'

The man's lawyer Alistair Haskett said his client was "outraged and very upset" about how he had been treated.

"The reason that he wanted to push forward and appeal the decision was that he felt this sort of treatment could happen to anybody not just to him... it wasn't about ducking a conviction or anything like that, it was about the decision being put right.

"He repeated that it was urgent, he was pacing up and down the booze bus.

"He experienced pain trying to hold his bowels and we was asked by one female officer if he was OK because he seemed to be unwell.

"There was lots of signs that he was in urgent need of using a bathroom but they weren't acted on at all."

Mr Haskett said he had come across similar mistreatment before.

"It's not altogether uncommon for police to mistreat motorists during this process. My read on it is that police seem to have an expectation or they seem to think they'll get away with it."

Police have been approached for comment.

