Former prime minister Malcolm Turnbull told the ABC's Four Corners program on Monday that he spoke to Mr Porter in December 2017 about reports the soon-to-be attorney-general had been seen drinking too much and "in the company of young women" at a Canberra bar.

"I said 'this is unacceptable conduct for a cabinet minister and it exposes you to the risk of compromise'," Mr Turnbull said.

He reminded Mr Porter that "Canberra was full of spies" and not all of them worked on behalf of Australia.

"The risk of compromise is very real - it's not just the stuff of spy novels," Mr Turnbull said.

Mr Porter, who still holds the portfolio in the Morrison government, denies the allegations and has labelled them defamatory.

"Four Corners' depiction of interactions in the bar are categorically rejected," he said in statement.

Former Liberal staffer Rachelle Miller, who was at the same bar with her former boss and then-lover, coalition minister Alan Tudge, witnessed the interaction and said Mr Porter's behaviour towards one woman was "clearly intimate".

At the time of the incident Mr Porter - now separated from his second wife - was married and his wife and young child were at home in Perth, the ABC reported.

Mr Porter said in a statement about his 2017 meeting with Mr Turnbull that the then-prime minister queried whether there was any accuracy to the "story" he had heard, and that the "answer was no".

"Malcolm then promoted me to attorney-general about two weeks after," Mr Porter said.

"In my time as AG I never had any complaint or any suggestion of any problem from Malcolm regarding the conduct of my duties as AG," although noted a disagreement about a citizenship issue shortly before Mr Turnbull's prime ministership ended.

The Four Corners program revealed that during his university days in Western Australia Mr Porter often made demeaning remarks about women, including notes in year books.

Barrister Kathleen Foley described his behaviour at the time as "deeply sexist and actually misogynistic".

"I apologise for material I wrote in a law school magazine 24 years ago. I obviously wouldn't write that now and it is something I regret," Mr Porter said.

Mr Turnbull said he was unaware of broader concerns about Mr Porter's behaviour towards women until he saw the Four Corners report.

"If I had known at the time what was broadcast tonight I would have made further enquiries before I made him attorney-general," Mr Turnbull said.

Ms Miller said while her relationship with Mr Tudge was consensual, she now wanted to speak about the overall "poor behaviour" within Parliament House.

"I lost a lot of self confidence because I didn't feel I had any power at all to stand up for myself," said the adviser, who has left Mr Tudge's office.

The minister for population, cities and urban infrastructure issued a brief statement after the program was aired.

"I regret my actions immensely and the hurt it caused my family. I also regret the hurt that Ms Miller has experienced," Mr Tudge said.

Mr Turnbull, who instituted the so-called "bonk ban" for ministers, said anyone who chose to take on a position such as cabinet minister must accept a high standard of behaviour and a "more circumspect" private life.

Australian Associated Press