The Court of Appeal is deciding whether the wording of police, when advising drink-drivers after breath tests, can be used as a defence.
Four drink drivers have been let off using the defence that the police stated the breath test could lead to prosecution - rather than conviction.
Until recently, police told drivers a failed breath test could be used as conclusive evidence in a 'prosecution' against them - while the law says they should be told it could lead to their 'conviction'.
In the Court of Appeal on Thursday, Crown lawyer Charlotte Brook said the purpose of the police advice was about explaining their procedural options to them.
"There's no material difference between the phrases conclusive evidence and a prosecution and conclusive evidence leading to a conviction."
But it has made a difference - it's successfully been used as a defence in some drink-driving cases.
There are reports up to 85,000 motorists who have been charged with drink-driving could seek to overturn convictions from the past six years.
Tiho Mijatiov, a lawyer assisting the court explained that failure to use the word 'conviction' meant drivers weren't aware they could be convicted.
"The purpose of these things is to bring home the gravity of the worst possible thing that could result," Tiho Mijatov said.
"Motorists are deprived of the informed choice to make a more advantageous decision."
The Crown argues police conveyed the right advice regardless.
The Court has reserved its decision.
