Prime Minister Scott Morrison is under increasing pressure to investigate a cabinet minister at the centre of a historical rape allegation.

ABC’s Four Corners on Friday reported the Australian Federal Police had been notified of a letter sent to the Prime Minister detailing an alleged rape in 1988 by one of Mr Morrison’s current cabinet ministers of a then 16-year-old girl.

Independent Senator Rex Patrick has called for the unnamed minster to be stood down – with a presumption of innocence – while the allegations are investigated.

“The matter that has been aired is a very serious one. It has sufficient grounds to see involvement by police forces and the South Australian coroner,” Senator Patrick told The New Daily. 

Senator Rex Patrick has called for the minister to be stood down while an investigation takes place. Photo: AAP

Prosecutors cannot pursue a criminal conviction because the woman’s death means the allegations cannot be tested, but Senator Patrick said the Mr Morrison should call an investigation.

“Whilst the presumption of innocence is important, the very serious nature of the allegation is such that the cabinet minister in question must stand down pending the outcome of any investigation,” he said.

To do nothing would open every cabinet minister to speculation, Senator Patrick said.

“That is the honourable thing to do. In the absence of such action, all other male cabinet members have a cloud over their reputations. If the Minister doesn’t want to do that, the PM should insist,” he said.

Greens Senator Sarah Hanson-Young said the shocking allegations should not be “swept under the carpet” and urged the prime minister to act to ensure the integrity of the government.

She said Scott Morrison’s silence on the matter was “deafening”.

The woman reported the allegation to New South Wales Police in February last year, triggering an investigation.

However, the investigation was dropped after the woman died by suicide in June.

The cabinet minster’s identity is not publicly known.

Labor Senator Penny Wong, who along with Greens Senator Sarah Hanson-Young and the PM received a copy of the letter, said she had been told of the allegations in 2019 after she “ran into” the woman in Adelaide.

“The complainant made an allegation that she had been raped many years earlier by a person who is now a senior member of the federal government. She indicated she intended to report the matter to NSW Police,” Senator Wong said.

“I said that making a report to the appropriate authorities was the right thing to do. I facilitated her referral to rape support services and confirmed she was being supported in reporting the matter to NSW Police.”

A coronial investigation into the complainant’s death is underway in Adelaide and the AFP has been notified.

Penny Wong said she had been made aware of the allegation in 2019. Photo: AAP

Senator Hanson-Young called on Mr Morrison to take action.

“He needs to make a judgement as to what he will do. The Prime Minister needs to say something and he needs to do something,” she said on Saturday.

Senator Hanson-Young called on the PM to act to ensure the integrity of his government.

“We can’t have a situation where such a horrific allegation of rape is levelled against a senior member of his government and no one does anything,” she said.

When Morrison government frontbencher Simon Birmingham was asked on Saturday if the accused should be identified, so as not to cast aspersions on the rest of the government, he said the matter should be left to the police to handle.

Minister for Trade Simon Birmingham said the matter should be left to police. Photo: AAP

“Everybody is entitled to natural justice and it’s important to back the police to do their job,” Senator Birmingham said.

“We back the police to do their job in this and every other instance.

“I don’t wish to see anybody lose their rights to natural justice.”

The AFP issued a statement on Saturday saying it has received a complaint relating to a historical sexual assault and will liaise with relevant state authorities.

“Further enquiries can be directed to the New South Wales Police Force,” the statement said.

“The AFP will not be making further comment.”

The explosive allegations come a fortnight after former Liberal staffer Brittany Higgins‘ claim she was raped by a senior Liberal adviser engulfed parliament and highlighted what some say is a ‘toxic’ culture.

Brittany Higgins’ alleged rape by a senior Liberal staffer has rocked the government.

Gender Equity Victoria chief executive Tanja Kovac said the “systematic sexism” in Parliament House needed to be cleaned up.

“But treating them as a one-off individual incident isn’t what is going to stop the behaviours,” she said.

“There is a systemic issue here. Its people in power misusing it in relation to people who have less power.”

There are four inquiries currently underway including a multi-party investigation into the culture.

Ms Kovac said the government needed to be held accountable for the culture and the findings of the inquiries.

“It appears to be a pattern of men in politics, in powerful positions, using their positions to take advantage of women,” she said.

“We don’t need it in this in parliament.”

Sexual assault support services:

• Canberra Rape Crisis Centre (24 hours): 02 6247 2525
• 1800 Respect national helpline: 1800 737 732
• Lifeline (24 hour crisis line): 131 114
• Beyond Blue: 1300 224 636