Major changes to New Zealand's legal system that became law yesterday are the start of a modernisation of criminal justice in New Zealand, Justice Minister Simon Power says.

Included in the changes are the removal of unanimous verdicts in jury trials and the doing away with witnesses giving evidence at pre-trial hearings such as depositions.

From this week, it will no longer be necessary for all 12 jurors to agree on a verdict. Instead, 11 will be sufficient to ensure an acquittal or conviction.

The other significant change will see evidence given at depositions - a hearing to determine if a case will go to trial - handed up in written form, instead of being heard orally.

Mr Power said the changes would mean a more swift delivery of justice that would not only address the needs of victims but would also produce cost benefits.

Victims would be spared having to give "distressing" evidence twice, although lawyers could still apply to a judge for oral hearings to take place.

The switch from unanimous verdicts to majority verdicts would reduce the number of trials by reducing the amount of mistrials. Mr Power said "rogue jurors" could cause delays in the system and allowing 11-1 verdicts would reduce the number of retrials.

The legislation allows for the Solicitor-General to review the law in two years to ensure it is working.

Leading defence lawyer John Haigh, QC, was part of a delegation who met Mr Power in an attempt to put on hold the changes to deposition evidence.

He said a compelling reason for the changes was a desire by the Government to save time and money, but he thought those savings could still be made by allowing depositions to continue.

Mr Haigh said the abolition of depositions could mean delays eventuating at trial, when new evidence emerged that would normally have arisen at an earlier hearing.

Depositions were also helpful as they allowed both defence and prosecution counsel the opportunity to test witnesses through cross-examination before trial, Mr Haigh said.

Defence lawyers could then prepare their cases depending on what arose at depositions.

Other changes include a change to double jeopardy allowing retrials in some cases; while a further change allows the District Court to hear P trials.