The greatest danger workers at Parliament House usually face is indigestion from a dodgy bain-marie casserole. So, even after Thursday's terror raids in Sydney and Brisbane, it came as a shock to Canberrans when they awoke to the screaming tabloid headlines: "PLAN TO ATTACK OUR PARLIAMENT."

As Prime Minister Tony Abbott confirmed on Friday morning, security agencies had picked up "chatter" of a potential attack on Parliament House. Australian Federal Police officers would now take charge of internal as well external security.

Parliament House is not just a building; it's a city within a city. Our temple to democracy has its own rules, its own conventions, its own economic ecosystem. There's a gym, a bank, a medical centre, a travel agent, a Post Office, a cafe. All there to service the needs of our politicians and those who orbit around them – the political staffers, the journalists, the public servants and the lobbyists.

The building's workforce swells to 5000 when Parliament sits. Keeping these people safe from harm is no light matter.

Yet no-one could deny the frisson inside Fortress Parliament on Friday. Suddenly, a building that, in non-sitting weeks, rivals Wagga Wagga Airport for excitement took on an air of danger and edginess.

Despite being a national icon, Parliament House has long been notorious for its lax security.

In 2012 a Russian national entered a restricted area of Parliament, bringing him within striking distance of then prime minister Julia Gillard. A security officer had not been rostered on to guard a particular door.

The breach led to a safety review. Yet two years later the wise folk at the Department of Parliamentary Services (DPS) decided to launch a 12-month trial of relaxed entry standards.

Previously, virtually everyone who entered the building had to be scanned by metal detectors and have their bags X-rayed. Under the new arrangement, hundreds of politicians, political staffers and departmental officers were allowed to sail through security with the swipe of a pass. Meanwhile, journalists, diplomats and the public were still subject to onerous checks.

This two-tiered system caused a scandal unseen in Canberra since Sky Whale was first hoist into the air. Politicians and journalists united to slam an arrangement that saw gallery doyenne Michelle Grattan screened for munitions while junior political staffers went unchecked.

Liberal senator Bill Heffernan was so incensed that he smuggled an imitation pipe bomb into the building and brandished it at a Senate committee hearing. The trial was promptly ditched.

Still, huge gaps remained. Only two unarmed security officers have protected the entrance to Parliament House's ministerial wing. Get past them and you would have access to the Prime Minister's courtyard, with a direct line of sight into his office.

Today it was different. An armed AFP officer stood outside the ministerial wing; inside, another watched over the PM's staff. Guided tour groups are now accompanied by security officers. And the "volume" on the security scanners appeared to be turned up. It is no longer possible to walk through the X-ray machines with keys and a pocket full of coins.

But there was no menace, no fear in the air. The sun blazed in a milky blue sky. We were alert but not alarmed.

The general public certainly wasn't. If anything, there were more visitors than normal. Flocks of uniformed school children - some in ties and blazers; some in trackie pants - sat around looking bored. Elderly couples posed for photos in the marble foyer. The gift shop did a roaring trade as tourists tossed up whether to buy a Paul Keating or Bob Hawke fridge magnet.

The cops seemed to be outnumbered by gardeners armed with mowers, leaf blowers and whipper snippers. They were prettying up the courtyards for Monday, when the politicians return for a fortnight of Parliament. New anti-terror legislation is top of the agenda.

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