The former male staffer to then-defence industry minister Linda Reynolds was shown the door in the wake of the alleged rape of Brittany Higgins in March 2019, which police are investigating.

Mr Morrison told reporters in Canberra on Tuesday: "It was the defence industry minister's office at the time and so there was some prior issues here and this final event was the one that triggered his dismissal."

As well, cabinet minister Simon Birmingham told a Senate estimates on Tuesday: "My understanding is there had been more than one security breach pertaining to handling of documents and access to the office after hours."

However, an estimates hearing was told on Wednesday the defence department was notified of only one "physical document" security breach in the office.

It occurred on March 19, 2019, just days before the alleged rape.

Senior defence official Katherine Jones was asked whether late-night access to Senator Reynolds' office itself constituted a security breach.

"From the perspective of defence, no," Ms Jones said.

Nikola Anderson, the security guard on duty on the night of the incident, said the pair had been provided with appropriate temporary passes, meaning entry into the office would not have constituted a security breach.

Labor frontbencher Tanya Plibersek asked Mr Morrison in parliament whether it was policy for the Special Minister of State to be told about all after-hours access to ministerial offices, or just specific instances.

The question drew on evidence given to Senate estimates hearing on Tuesday that then minister Alex Hawke had been advised by the finance department on March 26, 2019, Senator Reynolds' suite had been accessed after hours.

Mr Morrison told parliament caution needed to be exercised in responding to such questions, given police were investigating.

"What I will undertake to do for the member is to provide a response to that in writing ... after taking further advice," he said.

Australian Associated Press