This reservation is concerned with the circumstances in which unusual powers can be exercised for enabling effective rule in the event of a crisis. In practice this has often involved the deployment of the armed forces for example to provide essential services.
The main statutory provisions are set out in the Emergency Powers Act 1920.  This gives power for Her Majesty to declare a state of emergency and to make regulations by Order in Council for securing the essentials of life to the community e.g. for the preservation of peace, and for securing and regulating the distribution of food, water, fuel etc.
In addition servicemen may be employed under the royal prerogative in extraordinary circumstances to deal with particular crises.
Planning by the civil authorities for emergencies is not, however, caught by the reservation.
TABLE OF RESERVED MATTERS Head B - Home Affairs General