The Government is tightening legal aid rules - including making it harder for the wealthier to have legal aid for criminal cases - in an effort to clamp down on an expected $402 million blow-out over the next five years.

Among the changes will be:

* expanding the Public Defence Service across the country to take on 50 per cent of criminal legal aid cases

* bringing in fixed prices for certain cases

* a user charge of $100 for family and civil cases, excluding domestic violence, mental health and criminal cases

* narrowing the criteria for legal aid in family cases

* introducing income testing for less serious criminal cases

The changes are a first step in overhauling the legal aid system, and are expected to save $138 million over four years.

At the moment a single person earning more than $22,000 a year or an adult with two dependants earning more than $50,934 are not eligible for legal aid for family or civil cases. This will be extended to cover less serious criminal cases.

Applicants above the threshold can still apply for legal aid, but will have to prove that their case is likely to be an expensive one, or that they cannot afford a lawyer.

Changes to family cases

The rules for legal aid for family cases will revert to what they were prior to changes in 2006, which saw a 39 per cent increase in grants for care of children proceedings in three years.

The 2006 change saw the main criteria for legal aid grants become whether a child was involved, rather than the prospects of success for the case.

The "special financial circumstances" rule will remain, but will be narrowed to apply only for expensive cases.

Reverting to the old rules will not affect legal aid grants for more serious cases, Justice Minister Simon Power said.

More changes to come

He also signalled more changes later this year to the way legal aid applies to the Family Court, including closer scrutiny of counselling, specialist reports, how parties may contribute to costs, and whether legal aid should be available if the Crown is not a party in the proceedings.

Mr Power said the legal aid bill had increased over the past three years from $111m to $172m, and was forecast in five years to create a $402m hole in the legal aid budget.

"Two-thirds of the cost increase stems from the previous Government's decision in 2006 to extend eligibility for legal aid, and in 2008 to increase lawyer remuneration," Mr Power said.

"To be blunt, these changes were completely unaffordable and unsustainable then and they are even more so now."

He said the changes will not affect access to legal aid for vulnerable parties, care and protection of children, and serious criminal matters.

"But legal aid was never intended to be used to decide how many weeks a child spends on an overseas holiday, or to determine petrol costs associated with taking a child to school."

Work on expanding the Public Defence Service to take on 50 per cent of the criminal legal aid cases in Auckland, Hamilton, and Wellington over time is to take place from October.

The service will eventually be expanded to Tauranga, Hastings, Dunedin and Christchurch.

Fixed fees for certain cases will be introduced, including criminal summary cases, most family cases and some civil ones.

Other changes will be part of a bill to be introduced later this year, and the public will be invited to have their say through the select committee process. They are not expected to take effect until next year.