A word used by police when advising drink drivers of their rights is under scrutiny in the Court of Appeal this morning, with thousands of convictions potentially on the line.
The case hinges on the fact police had been using the word "prosecution" when advising drink drivers of their rights, rather than the word "conviction" - which is used in the legislation.
Lawyer Alastair Haskett earlier told Stuff the issue could affect about 85,000 motorists who have been charged with drink-driving.
Motorists who blow more than 400 micrograms of alcohol per litre of breath are held by the police.
The officer then reads a prepared script giving the detained driver an opportunity to phone a lawyer and have a blood test.
Until recently, the script advised the motorist their breath test result could be used as "conclusive evidence in a prosecution against you".
But the legislation stopped police from using the breath test as evidence unless the motorist was warned their result could be used as "conclusive evidence to lead to your conviction".
An Auckland District Court judge recently dismissed a charge of drink-driving against one of Haskett's clients, agreeing with the lawyer that there was a "material difference" in the meaning of the words "prosecution" and "conviction".
"The police have decided not to use the word Parliament requires, have directed officers to use the wording set out in Block J, have persisted with that despite at least two decisions of the district court dismissing charges for non-compliance with [the legislation] and the police have not appealed those two decisions," said Judge Russell Collins.
An internal police memorandum revealed senior police officers were aware of a potential problem when they were drafting the script, known as Block J, in 2014.
In the Court of Appeal in Wellington this morning, Crown lawyer Charlotte Brook said the purpose of the police advice was "not about bringing home to them the gravity of the situation, it's about explaining their procedural options to them".
For the motorists, this meant this was their only opportunity to take a further step to gather further evidence for their defence by taking a blood alcohol test.
She said the police position was that an infringement as opposed to a charge was also another kind of prosecution, so the use of the word prosecution covered both possibilities.
"The die has already been cast at that point because the breath test has already been obtained."
If the police wording was non compliant with the legislation then it was only non compliant "by a slim margin".
Lawyer Tiho Mijatov, who was appointed as counsel to assist the court, said it was important for proper processes to be followed.
"That's why there's that need for advice and for that advice to be accurate," he said.
"It's not just a matter of literally words being different, but they're not in strict compliance with the legislation in a material way."
Justice Stephen Kos questioned why it made a material difference to a motorist standing on the side of the road, and whether they would be able to understand the intended meaning – that they would likely end up being found guilty of drink driving.
"If they had messed up the word 'conclusive' the Crown would be in deep trouble," he said.
He asked whether the issue was the use of prosecution over conviction, when it was "'conclusive' that does the work here".
Mijatov said there was a social good in all people knowing what their rights were, and what the consequences were.
If the judges find in favour of the Crown, it will mean other people convicted of drink driving cannot use the same defence the previous successful cases have.
If they find against the Crown, it will leave the door open for potentially tens of thousands of drivers to appeal their convictions.
The court has reserved its decision.