Yes, but fortunately they do have armed guards to protect the important people who are in Parliament so the terrorist was shot after he stabbed the cop to death. He was an "ordinary people" cop, so he was unarmed.
Was this really a problem? He was killed with a gun by the second officer he came across. I did a little reading to see if Palmer had a gun as well, if he was surprised by the attacker or what, but have not found any detail like that.
By the second officer if he would have had a gun maybe just maybe he could have stopped him before the guy could have gotten to him.
The only reason there was an armed cop to get him after he stabbed the first cop to death was because they were near a building that had important people in it. If they were anywhere else it would have been just more ordinary people cops so they wouldn't have been armed and more people could have died.
I just don't know enough to know if another gun would have made a difference. It could be the first officer was surprised, in which case pulling a gun wouldn't be possible. It could be that without the element of surprise, a guy with a knife wouldn't be able to beat an officer with a baton. I know I don't like my chances facing a cop with a baton if all I have is a knife.