In March, security guards mistook a woman for a politician and allowed her to tailgate another vehicle into a private car park within the building.

According to reports, the woman then walked through the ceremonial entrance of the House of Representatives – reserved for politicians – without being asked for credentials.

The woman, who has not been named, had been invited to attend a function at Parliament House.

Committee chair and Liberal senator Cory Bernardi described the incident as a significant breach of security and complained about varying explanations from the department.

"In May 2015 it was claimed by [Erin Noordeloos, the assistant secretary of the Department of Parliamentary Service's security branch] that the person who tailgated was picked up [at] a security point," he said.

"In October that claim was changed by Ms Noordeloos to 'they made it no further than the front foyer'.

"Then, after October last year, an answer to a question on notice states that the person made it through security, was mistaken as being a member and was then escorted to a function in Parliament House by a member."

In a statement published on Tuesday, Department of Parliamentary Services secretary Rob Stefanic wrote that an investigation had been launched regarding the accuracy and consistency of evidence provided to the committee.

"I am writing to advise the committee that I have initiated an investigation into these matters," he said. "I will advise the committee further on this matter when the investigation has concluded."

"I also wish to advise the committee that [Ms Noordeloos] has submitted her resignation and this has been accepted."

A department spokesperson said the resignation was due to personal reasons.