Newshub can reveal the Government has no evidence to suggest that benefit sanctions on solo parents do anything to encourage wayward fathers to pay their share of child support.

In fact, it means the families are at higher risk of hardship and long term welfare dependency.

Currently people on a solo parent benefit can have their payment docked if they don't name the other parent of their child. In 98 percent of cases that's the father.

The penalty is $22 a week for each child, and an additional sanction of $6 a week for the continued failure to name the other parent.

The so-called section 70a sanction is aimed at getting child support payments from the absent parent.

More than three months ago Newshub asked the Ministry of Social Development to release, under the Official Information Act, any evidence that the sanctions worked.

MSD refused the request.

But it was forced to turn over more than 100 pages of material before the election, after the Ombudsman intervened.

The reports addressed to Social Development Minister Anne Tolley say, "We do not have sufficient evidence to confirm if the benefit reduction is achieving the policy's intent."

"Compared to other sole parents, clients affected by Section 70a have higher risk factors for long-term welfare receipt and hardship... sole parent families in general have the lowest living standards of all family types" and having access to the additional money on a weekly basis "would improve the social and economic position of these beneficiaries and their families."

A solo parent, who wants to remain anonymous, told Newshub her baby was born when she was just 15. She can't name the father and her benefit has been docked for more than five years.

The Auckland mother says that money could make a "huge difference" to her.

"I remember one time, I was at the supermarket... and I was standing there going, 'Do I choose toilet paper or do I choose washing powder'," she said.

"And I was thinking, 'I am in the middle of the supermarket right now, do I cry and break down here or do I wait until I go home and put my baby to bed, read him a story and then cry when he can't hear me anymore.

"I think $28 dollars in that sense could have made a difference and not only financially... I could have felt like a whole human being, which would have been nice."

National leader Bill English says he stands by the sanction on solo parents and will continue to do so.

"That's a long standing sanction... and it reflects the expectation of the public that the fathers of children... take responsibility," he told Newshub.

"There is a study going on now to further understand the impact of it, so we are happy with that."

Labour and the Green Party have committed to ditching the sanction.