Candice Preston and her husband Phillip Walker were found guilty of benefit fraud worth nearly $330,000.

A couple stood in the dock together charged with one of New Zealand's "very worst" cases of benefit fraud, but only one returned home to care for their four children.

Candice Lui Preston, a Nelson mother of four, was sentenced to two years and five months in prison for defrauding the Ministry of Social Development of $244,768 over 12 years.

It was described in court as one of the most serious cases of benefit fraud in New Zealand, and "certainly the highest" in the Nelson region.

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Preston's husband, Phillip Rangi Walker, was sentenced to nine months' home detention for defrauding the ministry of $84,915 over the same time period.

The couple stood in the dock at the Nelson District Court on Thursday together, having pleaded guilty last month to 42 benefit fraud charges.

The court heard that Preston was introduced to the "social welfare lifestyle" in 2001, when she was just 16.

Judge David Ruth said she has been on the "benefit treadmill" since then.

Preston's offending included forging letters purporting to be from a landlord and Walker's mother to obtain benefits, knowing that the information was false.

She also received a new $600 fridge freezer from the ministry after saying hers was broken. She advertised the new fridge for sale for $780 through an online trading site on the same day.

Preston also started a job at a fast food outlet while receiving benefit payments.

She was convicted of three charges of obtaining by deception, three of forgery, and 21 of using a document for monetary gain.

A ministry investigation found that Preston and Walker had been living together "in the nature of marriage" throughout the offending, while both submitted documents stating they were single.

Walker also continued receiving a benefit while working. He also received sole parent assistance while living with Preston and benefited from her fraud.

He was convicted of four charges of obtaining by deception, nine of using a document for financial gain, one of forgery and one of benefiting from fraud.

Preston pleaded guilty last month following a sentence indication from Judge Ruth of two years and five months' imprisonment.

Walker pleaded guilty following a sentence indication of 18 months' imprisonment with a "no promises" possibility that home detention would be considered.

Defence lawyer Michael Vesty said Preston's personal circumstances had changed since the indication and that home detention should be considered.

He said the publication of her photograph was a "very public punishment" that would have a "marked deterrent effect" for her and others. It would also impact on her four children, he said.

He said the threat of imprisonment over the past year has also served as a significant deterrent.

Preston was at a low risk of harm to the community and of reoffending, Vesty said.

"It is of great significance that Miss Preston, as a 16-year-old, was introduced to the benefit system," he said.

"She got into something when she was perhaps young and vulnerable and subject to some influence."

Walker said he took responsibility for introducing Preston to the welfare system.

Ministry lawyer Michael Crehan said Preston "actively managed and forged documents" to obtain money.

"She continued with this to maintain their lifestyle."

He said losses to the ministry amounted to more than $300 a week over 12 years.

Judge Ruth said: "This is among the very worst cases that the ministry has come across."

He said he had already applied discounts to her sentence for personal circumstances and guilty pleas, reaching an outcome that might be viewed as "overly generous".

He said any further discount was unjustified and sentenced her to imprisonment.

"I accept that your children will probably suffer more than anyone else in this process."

Walker was ordered to pay reparation of $10,000 at a rate of $40 a week. Judge Ruth said it was "futile" to order him to repay the full amount he had obtained.

"I think it's important that something be paid back to the community from whom, effectively, you have stolen."