A spokeswoman for the Association of Chief Police Officers said that each force decides on its own plan of action.
But she stressed that all forces adhere to the guidelines set out in The Manual of Guidance on Police Use of Firearms.
The manual states: "In any conflict situation a decision-making process is necessary to ensure that the conflict is dealt with in a logical and progressive manner.
"Information and intelligence received leads to a threat assessment.
"Then, following consideration of the relevant powers and policy, the appropriate tactical options are chosen to manage the threat and resolve the conflict.
"In spontaneous incidents the amount of planning will be commensurate with the level of threat and the time available."
In order to comply with European Charter Of Human Rights principles it must:
Have a legitimate aim
Be lawful
Be proportionate
Be justified
Be the least intrusive or damaging to the rights of individuals.
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