The call for Australian police to be given "shoot to kill" powers ramped up this week, in the wake of the London attack, the Brighton shooting and the coronial findings into the Sydney siege.

Former prime minister Tony Abbott and Liberal MP Andrew Hastie have both called for police to be given greater powers to shoot terrorists on sight.

They were promptly shut down by Prime Minister Malcolm Turnbull who said police in Australia already had the authority to shoot assailants.

New South Wales Premier Gladys Berejiklian has announced police will be given "shoot to kill powers" in the state.

So, how much will actually change in that state? And do other police around the country have the power to use lethal force?

Are police allowed to use their guns?

Police in all states and territories are armed with semi-automatic pistols.

The laws governing their use differ slightly in each state. But generally, police are allowed to use "such force as is reasonably necessary" to carry out their functions.

Vince Hurley is a criminologist at Macquarie University and says police are allowed to shoot an offender so long as they reasonably believe that person has, or is about to, seriously injure or kill another person.

"There is sufficient legislative power for the police to shoot an individual if they're going to cause harm to another person," he said.

What if police actually kill someone?

A police officer who has fatally shot an offender will be called to give evidence at a coronial inquest and will have to justify their actions under oath.

As long as the coroner is satisfied the officer was using reasonable force, the death will be considered a "justified homicide" and the officer won't face criminal charges.

Between 1989 and 2011, 105 people were shot dead by police in Australia according to a 2013 report by the Australian Institute of Criminology.

Nearly all were found to be justified homicides and only one was found to be an "unlawful homicide".

Why do police need 'shoot to kill' powers for terrorist attacks?

They don't. Most experts believe Australian police already have the legal authority to shoot terrorists if they are actively harming, or about to harm, members of the public.

Nick O'Brien is a counter terrorism expert at Charles Sturt University and says police are trained to shoot the largest area of an offender's body, the torso or trunk.

"If you shoot someone in the trunk you'll hit a vital organ and that person is likely to die," he said.

"Effectively, you're shooting to stop and I think it's a better sell to the public to say that the police are shooting to stop, rather than shooting to kill."

Sorry, this video has expired NSW Coroner Michael Barnes hands down findings into Sydney siege

Why are politicians calling for police to have special powers?

This debate has been sparked by the coronial inquest into the 2014 Sydney Siege.

The police snipers who had their rifles trained on the Lindt Cafe reported having a clear shot of gunman Man Haron Monis about 7:35pm on December 15.

But they told the inquest they didn't shoot because at that stage Monis hadn't harmed any of the hostages and the snipers didn't think they could legally justify a "kill shot".

Professor O'Brien believes the legal protection for those snipers already exists and says they could have justified their actions.

"The important thing is that someone has got to make that judgement," he said.

"Someone has got to say, 'I believe that Man Haron Monis or whoever is going to kill hostages and this is the reason why I believe that'.

"You've actually got to make that judgement before someone can pull the trigger."

So, police don't need additional protections?

Not exactly. The "shoot to kill" slogan being peddled by politicians is simplistic and fails to acknowledge that there are still grey areas in the law.

Mr Hurley believes there's a significant difference between a police sniper taking an intentional "kill shot" and an officer using their gun in a split-second decision to protect someone from harm.

Mr Hurley said the snipers had a belief they could be charged with murder under the NSW Crimes Act because they would be intentionally killing Monis, as opposed to simply trying to stop him with "reasonable force".

"There is a legal and ethical conflict," he said.

"The legislation almost contradicts itself … it certainly muddies the water regarding the police power to be able to go and execute someone in a controlled police environment.

"In a situation [like the Lindt siege] that was being controlled by police … where Monis had de-escalated what was happening inside the stronghold, the police felt they were not legally allowed to execute him in anticipation of what else he might do."

How do we resolve this conflict?

The question we as a society need to ask ourselves is: How comfortable do we feel allowing police to use pre-emptive deadly force to protect us from terrorism?

The NSW Coroner recommended changes to the NSW Terrorism and Police Powers Act to give police sufficient legal protection to respond to terrorist incidents "in a manner most likely to minimise the risk to members of the public".

That recommendation is broad and open to interpretation.

The NSW Government has said it will accept all 45 recommendations from the coronial inquest, with Ms Berejiklian arguing police in her state would now have legal protections if they shoot a terrorist dead.

One thing is clear, the threat of terrorism isn't going away anytime soon.