The prime minister has ordered a review into the use of guns by police in England and Wales following the Paris attacks, the BBC understands.
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.
Labour has warned of possible damage to community relations with the police.
Gunmen and suicide bombers killed 130 people in Paris when they attacked a concert hall, a major stadium, restaurants and bars almost simultaneously on 13 November.
BBC political correspondent Chris Mason says the atrocity has provoked deep soul-searching within government and among the police, raising the question of how the UK would cope if something similar were to happen here.
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.
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.
Currently, the Criminal Law Act 1967 allows police to use “reasonable force”, while the Criminal Justice Act 2008 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, around 6,000 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.
An officer must also determine how immediate and grave a threat is, and whether any action short of using force could be deployed instead.
The Criminal Justice and Immigration Act 2008 says that what amounts to reasonable force should be considered in light of the circumstances a police officer is faced with – and what they honestly and instinctively believed they were faced with – at the time.
Tony Long, a former specialist firearms command officer who was cleared of murder in July, 10 years after shooting dead suspected armed robber Azelle Rodney, said police were not asking for additional powers.
“I think they’re just asking that when they’re investigated they are not automatically treated as suspects, because in the eyes of the police officer, he’s done what he’s been trained to do.”
He added: “If you perceive as a result of a suspect’s actions that your life or somebody’s else’s life is in danger, then you have to react. And you react in accordance with your training.”
A government source said terrorist incidents at home and abroad had shown “the life and death decisions police officers have to make in split-second circumstances”.
“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.”
‘Held to account’
But Jeremy Corbyn told the Sunday Times that any moves to weaken oversight of firearms use would “diminish” public confidence in the police.
“There has to be a very robust and strong independent inquiry into what the police do. Like any other public organisation, they must be held to account. I hope this is not a political stunt.”
Following Paris, Mr Corbyn told the BBC he was “not happy” with police operating a shoot-to-kill policy, but later backtracked, insisting he supported any “strictly necessary force”.
His shadow business secretary, Angela Eagle, told the BBC there must be “safeguards” to prevent wrongful shootings, but added: “We also need to give our armed police the confidence if they are dealing with a marauding terrorist… they can get that person down and get them on the ground and save life.”
The Met Police are also planning to increase the number of officers able to use Tasers.
The prime minister is thought to be in favour of the move in light of the response to the recent stabbings at Leytonstone Underground station, in which a Taser was used.