Scott Morrison says he will “not indulge in extrajudicial processes” despite calls for an independent inquiry into an historical rape allegation levelled against Christian Porter.

The Attorney-General has been accused of raping a 16-year old in 1988, an allegation he emphatically denies.

The alleged victim took her own life in 2020, a day after informing she no longer wanted to pursue the complaint.

The Prime Minister has faced growing calls to launch an independent inquiry into the allegation after NSW Police declined to investigate it, citing “insufficient admissible evidence”.

Mr Morrison backed a coronial inquiry in South Australia, where the woman died, if “coroners see fit”.

But he told reporters on Tuesday he would “not indulge” the idea of an independent probe, arguing it would undermine equality before the law.

“There is not a separate legal process that applies to the Attorney-General or anyone else. There’s only one rule of law here,” he told reporters on Tuesday.

“I’m not going to indulge in other extrajudicial processes that suggest that one Australian is subject to a different legal process to any other Australian.

“If we do that, we are eroding the very principles of the rule of law in this country. There are not two laws in this country.”

But Labor frontbencher Tanya Plibersek dismissed the claim as “nonsense”, citing an investigation into sexual harassment allegations against former High Court judge Dyson Heydon.

Labor and the Greens have called for an independent probe. Nationals MP Barnaby Joyce broke ranks on Monday, saying the move was necessary to avoid a media “mosh pit”.

Ms Plibersek said Australians needed to be convinced Mr Porter was fit to hold his role despite no formal police investigation.

“We have a very serious allegation against the first law officer of the land. He needs to be above reproach and beyond doubt, and tragically the complainant in the case is not here to pursue all legal avenues herself,” she said.

She also accused the Coalition of hypocrisy, saying they weaponised an inquiry into whether former prime minister Julia Gillard had used union money to pay for a home renovation in 1994.

“This is a government that spent $86m on a royal commission into whether Julia Gillard’s boyfriend built her bathroom 30 years ago,” she said.

With rapes under-reported and convictions rates low, Ms Plibersek said victims needed to be given confidence in the legal system.

“Let’s see some reforms that would make it a little easier to make these claims and a little fairer when it comes to properly determining what’s happened,” she said.

It comes after revelations the alleged victim told a counsellor about the allegation in 2013 aired on the ABC’s Four Corners on Monday.