Scotland Yard has told the public that suspected rioters and looters can be hit with weapons if they are honestly thought to pose a danger.
In a document sent to businesses in the capital on Wednesday, police gave explicit guidance on what constitutes "reasonable force", saying people do not have to wait to be attacked, if they are in their own home or business.
With police numbers stretched to the limit, the Metropolitan police said if someone "honestly and instinctively" believed they, their business or another person was in danger, they could use force.
The guidance adds that a weapon can be used and says: "The more extreme the circumstances and the fear felt, the more force you can lawfully use in self-defence."
The Met guidance says use of a weapon could also be lawful and constitute reasonable force, even if the person attacked proves to be innocent.
It is understood the guidance was issued after business owners asked for advice about how much force they could use to defend themselves and their property.
The police guidance is contained in a document called "MPS disorder update for business", which was sent out on Wednesday afternoon.
In a passage on reasonable force, the Met says: "Anyone can use reasonable force to protect themselves or others, or to carry out an arrest or to prevent crime.
"You are not expected to make fine judgments over the level of force you use in the heat of the moment. So long as you only do what you honestly and instinctively believe is necessary in the heat of the moment that would be the strongest evidence of you acting lawfully and in self-defence.
"This is still the case if you use something to hand as a weapon.
Police tell public rioters can be hit with weapons if they pose a danger | UK news | guardian.co.uk