Two cops under investigation after a judge slammed evidence they gave against a man convicted on driving charges.

Police and the Independent Police Conduct Authority have begun investigating the Palmerston North-based officers after High Court judge Jillian Mallon expressed concerns over erroneous evidence they gave at a defended hearing last year.

Justice Mallon upheld an appeal by the driver, Damon William McKelvey, who was convicted of failing to stop and dangerous driving after driving away from the officers in Levin.

They are also under investigation for failing to disclose information to defence lawyer Brian Gore that almost certainly would have led to a not guilty verdict.

The investigation follows the case of former Alexandra police officer Neil Ford, who was sentenced to two years and four months' jail for perjury after lying about a car accident that he caused in 2005.

Ford's lies led to Shane Cribb being convicted of causing the crash.

McKelvey was found guilty and sentenced to 60 hours' community work after he was convicted last year.

He was also disqualified from driving for nine months.

At his defended hearing the officers gave similar evidence about the route McKelvey drove and the speeds he travelled - between 60km/h and 80km/h in a residential area.

However, he appealed after a recording of the officers and the police communications centre contradicted their in-court evidence.

The recording had not previously been disclosed to Gore, despite him specifically requesting it.

On the recording one of the officers can be heard saying McKelvey's manner of driving was "excellent actually".

"The recording is relevant and ought to have been available to Mr McKelvey before the defended hearing took place," Mallon said.

"The recording casts, at least, real doubt on the officers' evidence. The recording ... shows that the officers gave completely incorrect evidence as to the route of the pursuit. This casts doubts on other aspects of their evidence, including the speeds at which Mr McKelvey was driving and whether he was driving in a dangerous manner."

Prominent Auckland defence lawyer Barry Hart said it was common for judges to dismiss entire cases if police had failed to provide full disclosure.

He said lawyers needed to be vigilant and proactive when asking police for information, listing specific things and chasing up anything that is not handed over.