A prominent Westport lawyer has escaped a fourth drink-driving charge, despite being over the limit, because he was breath-tested on private property.

Doug Taffs, 59, was caught by police on August 19 with a breath-alcohol reading of 480 micrograms.

Police attempted to pull him over about 200 metres from his house but followed him on to his property when he failed to stop for their flashing lights.

Judge Michael Behrens dismissed the charge because the police conducted the breath test on private property.

''I find that New Zealand citizens have an expectation that police will not come on to their land and randomly breath-test them,'' he said.

''I believe the evidence was improperly obtained.''

Senior Constable Donald Abbey and Constable Greg Sherie had been driving to Granity when they spotted a Land Rover travelling along Fairdown Rd.

The car had not breached any traffic rules, but Abbey said:''I bet he's come from the pub.''

They did a U-turn to give a random breath test, but Taffs did not stop.

He continued up the road about 200m before entering his driveway and parking by his house.

The police followed the car on to Taffs' property.

Taffs told the court he never saw the flashing lights, but Sherie said ''any reasonable motorist'' would have seen them.

The judge said he was not prepared to say Taffs had seen the police lights and believed his ''surprise and concern'' at finding the officers in his driveway was ''genuine''.

After failing a breath test, Taffs was taken back to the Westport police station, where an evidential breath test confirmed he was over the limit.

''When I spoke to the defendant he admitted he had been drinking and I could smell alcohol on his breath,'' Sherie said.

In conducting the test, the policemen were acting on an ''implied licence'' that entitles them to enter a property and knock at the front door, provided they are there for a lawful purpose.

If they are asked to leave, they must.

Sherie said he knew he was on private property but was not asked to leave.

Judge Behrens ruled that the police did not have the right to test Taffs on his property.

''Constable Sherie was intent on beginning breath-testing procedures because the decision to do so had been made before he entered on to Mr Taffs' property. He did not consider whether he could go on to the property or not,'' Judge Behrens said.

He dismissed the charge, saying public interest did not outweigh privacy, particularly on a police officer's whim ''with absolutely no grounds for a belief ... that a motorist has been driving with excess alcohol on his breath''.

Taffs declined to comment today, but his lawyer, Pip Hall, was pleased with the outcome.

''The judge followed established legal precedent and what it is saying is that the police have no right to gather information in that way," he said.

Taffs has three drink-driving convictions, including an incident where he hid coins in his mouth in a bid to beat the breath-testing machine.

After being stopped for drink-driving last year, Taffs was taken back to a police station, where he was found trying to escape by climbing over a back wall.

He then tried to disengage the breath-testing machine by unplugging its power cable and hiding a cord in the drawer of a filing cabinet.

Police put the cord back into the machine, but when Taffs took the test, silver coins fell out of his mouth.

He recorded a blood-alcohol reading of 115 millgrams of alcohol per 100 millilitres of blood.

At the time, Taffs said he ''lost the plot'' and had acted ''like a complete prat''.