Fundamental pillars of the criminal justice system may be eroded whichever party wins the election this year, as both National's and Labour's proposals would look into changing the right to silence or the presumption of innocence in rape cases.
Both major parties claim the current system is not upholding justice for victims, and are looking at changes that would effectively make it easier for prosecutors to obtain convictions.
National wants to explore allowing a judge or jury to see an accused's refusal to give evidence in a negative light, while Labour wants to shift the burden of proof of consent from the alleged victim to the accused.
Auckland University law professor Warren Brookbanks said both policies challenged two fundamental principles: the right to silence, and the presumption of innocence, which are both protected in the Bill of Rights Act.
Of National's plan, he said: "It's an intrusion into the right to silence.
In the trial process, offenders are in any event always at a serious disadvantage relative to the prosecution, and there are some important protections in the trial process, and the right to silence is a fundamental right. These are part of our democratic rights that apply to all citizens."
Regarding Labour's proposal, he said reforms in the 1980s already meant that an accused had to show an "honest and a reasonable belief" that the victim was consenting.
"It means they have to have made some inquiry as to the attitude of the other person. And if they haven't, then they are acting unreasonably and are going to be convicted."
Professor Brookbanks said shifting the burden of proof would made it even harder for defendants, especially because it is often one person's word against the other person's word.
"Usually in these cases, there are no witnesses. Who do you believe? The defendant has to go the full distance of proving to the satisfaction of the court that it's more probable than not that the victim was consenting. That is a very difficult threshold to reach."
He said both parties' proposals had the potential to capture the innocent.
"Innocent people get caught up in the system, and these provisions affecting the right to silence and the presumption of innocence are there to ensure the prosecution has enough evidence to justify bringing a charge."
Labour's justice spokesman Andrew Little did not think the party's proposal would lead to more innocent people being convicted.
"I don't see why. You're assuming that there is a propensity to lay false complaints. There is no evidence pointing to that."
He said eroding the right to silence went too far, but Justice Minister Judith Collins said the same of Labour's proposal.
"The presumption of innocence is fundamental to our justice system and our society. Requiring an accused person to prove their innocence would undoubtedly result in many injustices and wrongful convictions."
Rape and sexual violence cases:
The right to silence: National wants to explore allowing a judge or jury to take an adverse inference if a defendant refuses to give evidence
Presumption of innocence: Labour wants to shift the burden of proof of consent to the defendant