Senator Michaelia Cash also insisted the alleged rape of one political staffer by another would not be "politically embarrassing", describing it as "something that would need to be attended to" rather than hidden.

The Liberal senator for Western Australia said that on Monday when she gave evidence in the ACT Supreme Court trial of Bruce Lehrmann, who is accused of raping Ms Higgins in March 2019.

Lehrmann, 27, has pleaded not guilty to a charge of engaging in sexual intercourse without consent.

He denies any sexual activity with Ms Higgins in the office of Senator Linda Reynolds, who was their boss at the time, after "a drunken night out" that culminated in the pair attending Parliament House.

Ms Higgins left Senator Reynolds' employment and started working for Senator Cash, who gave evidence via audio-visual link from a remote location, about two-and-a-half months after the alleged rape.

Ms Higgins has previously told the court she had "many conversations" with Senator Cash about the alleged sexual assault while working for the politician between June 2019 and her resignation in January 2021.

Senator Cash denied this on Monday, saying she first spoke to Ms Higgins in October 2019 about "a security breach" that had occurred when the latter had worked for Senator Reynolds.

She said Ms Higgins and her chief of staff, Daniel Try, had come to talk to her that month after The Canberra Times made an enquiry about what had happened in Senator Reynolds' office in March 2019.

According to Senator Cash, Ms Higgins was embarrassed because "it related to herself" and another then-staffer for Senator Reynolds attending Parliament House while intoxicated after a night out.

She said she was informed Ms Higgins had fallen asleep on a couch in Senator Reynolds' office and later been found there by security, denying any knowledge of a sexual assault allegation at that time.

Prosecutor Shane Drumgold SC suggested to Senator Cash that she had actually been "fully aware" in October 2019 that Ms Higgins alleged she had been raped by Lehrmann seven months earlier.

Senator Cash rejected the proposition, saying she "always thought it was a security breach" until Ms Higgins resigned in early 2021 and disclosed "a sexual element" during a phone call a few days later.

Mr Drumgold subsequently put it to Senator Cash that she was denying prior knowledge of the alleged nature of the incident because it would be "politically embarrassing" for the former Coalition government if it became public knowledge that one of its staffers had been accused of raping another.

Senator Cash replied that this was "absolutely not" the case.

"I don't know how it could be politically embarrassing," she said, also saying she could not "understand a political connection to this".

Under cross-examination by Lehrmann's barrister, Steven Whybrow, Senator Cash agreed with the proposition it would be "political suicide" to try covering up "a sexual assault between staff".

"Correct, hence my confusion with the previous line of questioning," Senator Cash said. "Absolutely."

The senator added that, during the initial discussion with Ms Higgins in October 2019, the latter had been "adamant the entire matter had been dealt with at the time".

Senator Cash told Mr Whybrow the matter was never raised with her again until February 2021, days after Ms Higgins resigned from her office "out of the blue".

She said that month was when she first heard the word "rape" mentioned in connection with what she had always believed to be nothing more than a security breach.

Asked whether she had ever sought to prevent Ms Higgins going to police to report the alleged sexual assault, she replied "absolutely not".

Mr Try gave similar evidence on Monday, also denying he knew in October 2019 that there were allegations the "security breach" incident had involved Ms Higgins being sexually assaulted.

He went on to dismiss the suggestion his primary concern, upon being informed of the incident seven months after the fact, had been to protect Senator Cash against any political fallout.

"That's not true at all," Mr Try told the court. "I was worried about Brittany."

Sam O'Connor, a member of the Queensland state parliament and a friend of Ms Higgins, later appeared via audio-visual link on Monday to tell the court of how she had disclosed the alleged rape to him.

Mr O'Connor recalled being "pretty angry" about what Ms Higgins told him was "a super f---ed up thing that happened".

He said he had encouraged Ms Higgins to report the alleged rape to police, but she was initially worried "this would define her [and] she would be known for this instead of being good at her job".

The trial continues.

MORE COVERAGE OF THE TRIAL: