Liberal senator Bill Heffernan has smuggled what appeared to be a "pipe bomb" into Parliament House to make a point about declining security standards in the iconic building.
And the head of the Australian Federal Police, Tony Negus, has admitted the ingredients needed to create such a bomb could be smuggled into the building.
Senator Heffernan has been warning for months about a rising security risk facing the $1.1 billion building, which opened in 1988.
The Department of Parliamentary Services last week began a 12-month trial of new security arrangements under which hundreds of MPs, senators, political and departmental staff no longer need to be scanned by metal detectors, or have their bags checked.
Diplomats, journalists and members of the public are still checked.
The measure is designed to save the department money, speed up entry and allow internal security staff to be deployed away from entrances and to other areas of the building.
In practice, though, more security staff have been required at the building's entry points to enforce the new system.
Senator Heffernan brandished the "pipe bomb" while asking questions of Mr Negus. It is understood the senator brought in a replica of a pipe bomb, not an actual pipe bomb.
"Up until this point, most people working in this building know that it is safe but I don't think it any longer and to demonstrate that this morning what could be ... I brought this through security, a pipe bomb," he said.
"When I was a kid we used to blow stumps out on the farm, 50 years ago. We'd get some nitropril, a quart of distillate, a plug of jelly and a detonator, light the bloody thing and [it would] go to buggery. It could blow a tree the size of this building out of the ground."
Parliament House in Canberra has 4700 rooms and sits on a 32-hectare site.
"At the present time there is nothing to stop anyone from bringing those ingredients in here over a period of time through security, would you agree?" Senator Heffernan asked.
Mr Negus responded: "Senator, under the current arrangements, that is a risk, yes."
Mr Negus went on to say that the federal police, who provide security for the perimeter of Parliament House, had raised security concerns with the department of parliamentary services.
"We have been in regular consultation with them through the Attorney-General's department, we have briefed the presiding officers of the Parliament on our concerns and what we would put forward as an appropriate level of security," Mr Negus said.
Senator Heffernan added that the security arrangements at the building's entrances acted as a "speed camera" arrangement.
The senator has a history of concern for parliamentary security.
In February, he suggested the building should be shut down in the context of current budget cuts.
In 2009, Senator Heffernan had a knife confiscated from him at NSW Parliament, which he said he had brought in to test security.
In a separate estimates hearing, Carol Mills, the head of Department of Parliamentary Services, which is running the trial, confirmed that the changes would save $400,000 on screening costs among a $3-million saving on security in general under the new arrangements.
But she also confirmed under questioning by Senator Heffernan that DPS was currently spending $1.8 million on her office refit.
Senator Heffernan, who described the changes as ''stupid, dodgy and risky'' said: ''My message to the Department of Finance is get your priorities right.''
Senator Penny Wong later questioned why a veteran journalists' like Michelle Grattan is still screened on her way into Parliament, but parliamentary and ministerial staff with decades less time in parliament are not.
The hearing continues