The United Kingdom Prime Minister, David Cameron, has ordered a review of the use of guns by police in England and Wales following the Paris attacks.
The review will examine whether the law gives enough support to officers making a "split-second" decision to shoot.
It follows concerns from senior police that firearms officers do not have the necessary legal or political backing to work with confidence, and comes on the heels of the killing of 130 people in Paris by gunmen and suicide bombers in a barrage of attacks on 13 November.
Of the 130,000 officers in England and Wales about 6,000 are trained to use guns, but the government has announced plans to significantly increase that number.
Metropolitan Police Commissioner Bernard Hogan-Howe is understood to have raised concerns with David Cameron about the legal position of armed officers.
The issue was also discussed at a National Security Council meeting on counter-terrorism last week.
Currently, Britain's Criminal Law Act allows police to use "reasonable force", while the Criminal Justice Act recognises the defence that an officer had an "honest and instinctive" belief that opening fire was reasonable.
The internal review - to be carried out by the Home Office, the Attorney General's office and the Ministry of Justice - is expected to examine whether those laws go far enough to protect armed officers and prevent them hesitating in the event of an attack.
Of the 130,000 officers in England and Wales, about 6000 are trained to use guns, but the government has announced plans to significantly increase that number.
A firearms officer was arrested last week over the fatal shooting of Jermaine Baker, 28, in Wood Green, north London. The Independent Police Complaints Commission is also investigating the incident.
There have been warnings that fears of lengthy investigations, public inquiries and even prosecutions following a shooting could deter police officers from taking up firearms roles.
Labour has warned of possible damage to community relations with the police. Labour MP Angela Eagle said there could not be a shoot to kill policy without democratic involvement.
"There have to be safeguards, because we know what happens when people are shot wrongly, and we saw that with Jean Charles de Menezes (a Brazilian man shot dead by police after he was wrongly deemed to be involved in a bombing attempt in the wake of the deadly London bombings of July 2005).
"But we also need to give our armed police the confidence, if they're dealing with a marauding terrorist of the sort we saw in Paris - that they can get that person."
When can the British police use force?
Officers must consider whether the use of "reasonable force" has a lawful objective and basis. Their options include: self-defence, defence of another person, preventing damage to property and preventing a crime.
An officer must also determine how immediate and grave a threat is, and whether any action short of using force could be deployed instead.
A government source said: "We must make sure that when police take the ultimate decision to protect the safety of the public they do so with the full support of the law and the state - there can be no room for hesitation when lives are at risk."
Liberal Democratic leader Tim Farron said police officers "must feel protected", but the law must be reviewed "in a calm and collected manner and not in a knee-jerk response to terror attacks".
The Metropolitan Police are also planning to increase the number of officers able to use Tasers.