Theresa May has chaired a meeting of the Government's emergency committee COBRA in response to the terror attack in London.
:: What is COBRA?
COBRA - which stands for Cabinet Office Briefing Room A - is the mechanism used for ministers and officials from across Whitehall to meet in response to major events and emergencies.
:: Who attends the meetings?
It varies depending on the situation. In response to a terrorist incident such as in London, the intelligence and security agencies will usually attend to provide updates on the latest information they have, while senior police officers will also be present.
:: Apart from police and spymasters, which politicians attend?
Senior ministers from relevant departments attend the meetings in Whitehall along with top officials.
:: Does the Prime Minister always chair COBRA meetings?
No, other members of the Cabinet or senior ministers can lead the meetings when appropriate. But the decision by Mrs May to chair this meeting is an indication of the severity of the incident and a sign that she wants to personally lead the Government's response.