The police could have a huge miscarriage of justice on their hands, after the discovery of faulty breathalysers.

Four hundred breath testers have been recalled, with police promising to waive infringements and charges, and withdraw prosecutions resulting from the devices.

But lawyer Karen Harding said if someone's already been jailed, that conviction cannot be withdrawn - it must be appealed and quashed in a higher court.

She said the police need to identify each person who has been mistakenly prosecuted.

"They need to front up to these people directly. They'll have to find them because otherwise there's a huge miscarriage of justice."

Harding said those people will likely already have been punished.

"If you plead guilty in July you could have been sentenced in September. There could've been people who have gone to jail, which is quite serious, and then there's the home detention and the community detention people."

Karen Harding says some people will have had cars confiscated, resulting in job losses, financial hardship and relationship breakdowns.