David Cameron has ordered a review on the use of guns by police in England and Wales.

The prime minister is said to be concerned the law doesn't offer enough protection for armed officers who make the decision to shoot.

Following the Paris terror attacks, the Government's trying to work out how the UK would cope if something similar happened here.

Newsbeat's been looking at what "shoot-to-kill" actually means.

What are the rules?

It comes down to the law of self defence or defending others in a threatening situation.

If the police or military believe there is a threat to life, then it may be appropriate to shoot someone.

An example of this could be an attacker wearing a suicide belt with hostages.

The Home Office told Newsbeat: "Operations involving firearms will be intended in appropriate circumstances to bring an end to an imminent threat to life or of serious injury.

"However, the use of force must be justified under the law, and must be reasonable in the circumstances."

Is there actually a 'shoot-to-kill' policy?

Shoot-to-kill is not a policy but an action that may be required if there's a threat that endangers other peoples' lives.

Police are trained to do whatever it takes to neutralise a threat.

The UK's police forces do not have a blanket shoot-to-kill policy however police can be legally justified in shooting at the head even if the attacker ends up dead.

The Home Office says: "Under the Criminal Law Act 1967, the use of force for the prevention of crime and apprehension of offenders and those unlawfully at large must be 'reasonable' in all the circumstances.

"It may be for a court to decide whether that was the case."

Some human rights lawyers think there is no need to use the phrase. Barrister Matthew Stanbury told Newsbeat: "If the police are faced with an armed terrorist, they can act in defence of themselves or the public, as long as they act reasonably.

"It is difficult to imagine any circumstances in which a police officer faced with an armed terrorist would not be acting reasonably by shooting to kill him."

Whose responsibility is it to make the decision?

Firearms operations are normally authorised by senior officers.

It is the individual officer's call whether he or she pulls the trigger.

That officer must be able to justify, under the law, that their action was reasonable force to protect themselves or others.

Government ministers would never be able to tell an armed officer how to respond to a specific situation they are dealing with.

Have there been problems in the past?

The death of Jean Charles De Menezes shows what happens when the intelligence is wrong.

Jean Charles was an innocent electrician who was shot in the head seven times in a tube carriage in London, two weeks after the 7/7 bombings in 2005.

Officers who opened fire told an inquest they genuinely believed he was a suicide bomber.

There was an open verdict and a decision that no officer should be prosecuted.

Earlier this year, an officer was found not guilty of murder after shooting dead a suspected armed robber. The jury had not been told an inquiry had previously found he had no reason to open fire when he did.

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