NZ Police dog Tasman "Tas" is the only cross-breed animal in service with (inset) her police officer Matthew Fage.

Three years ago, she was leading a life of crime, stealing tennis balls from a court in Blenheim and mastering the game 'catch me if you can'.

Now, a stray, cross-breed saved from a life of homelessness has overcome a stroke to become one of the country's best drug dogs.

Tasman, who was first named Banjo, belonged to no-one when she was eventually caught and taken to a pound. There, she was given a seven-day death sentence.

But something about this brown and white pooch gave her a life extension and that's when the police dog handlers received a call.

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The pound explained they had a stray that seemed to have the qualities of a detector dog, but wasn't what the force was used to. All detector dogs are either labradors or shepherds.

Put through some simple drills the police took her on the spot and she was later flown to the police Dog Training Centre at Trentham, Upper Hutt.

At the same time, senior constable Matthew Fage was about to begin a nine-week drug course. He would be partnered with a new dog after his last working companion suddenly died.

Fage was asked to train a german shepherd and Banjo who was set for a future in Rarotonga as a drug detection dog.

Training wasn't smooth sailing but Banjo was meeting her targets. In the end, she ran rings around the other dog, graduated, and Fage decided to take her on.

She needed a name and Fage settled on "Tasman".

Having been a dog handler for 19 years, working with german shepherds, Fage said the pair received some sideways glances. Colleagues would tease, "It's not bring your pet to work day".

She's a real character with a zest for life but Fage could tell she was a victim of abuse.

"[For] some of our commands, we raise our hands and the sight of that used to make Tasman cower and urinate herself as she thought that she was about to get hit," he said on the Wellington Police Facebook page.

"She's well-loved now and grown out of it but it's very sad to know what she potentially went through in her past life."

Tasman had only been working with the police for under a year when she became paralysed one morning, dragging her back legs.

Fage rushed her to the vet who weren't sure what had gone wrong. It turned out Tasman had suffered a stroke of the spinal cord and there is no cure.

But there's hope that in time she will overcome her disability. The movement in her right leg came back about an hour after Tasman's stroke.

With a lot of dedication and care, Tasman is on the mend. Her left leg is now 90 per cent functional.

Last September, Tasman and Fage were selected to compete at the NZ police dog's national trials where the top two detector dogs from the police, customs and corrections compete for the title as the best drug dog in the country. They placed second.

​Tasman is now the only non-pedigree New Zealand police dog as all other patrol dogs are either german shepherds and are supplied by the police dog breeding programme based at the Dog Training Centre near Wellington.

Patrol dogs are mainly used to track and search for people while many of them are also trained for search and rescue, victim recovery, Armed Offender Squad duties and drug detection.

Detector dogs are are trained to sniff out narcotics, firearms, currency and explosives and are mainly german shepherds or labradors but springer spaniels and cross breeds are used too.