The exact grounds for such a proclamation by the monarch are defined in the Act as: ...any action has been taken or is immediately threatened by any persons or body of persons of such a nature and on so extensive a scale as to be calculated, by interfering with the supply and distribution of food, water, fuel, or light, or with the means of locomotion, to deprive the community, or any substantial portion of the community, of the essentials of life...Upon a proclamation, Parliament must meet within five days and the Act gave His Majesty in Council, by Order, to make regulations to secure the 'essentials of life to the community' and gave the relevant Secretaries of State the power for the 'preservation of the peace' and the 'essentials of life' as defined above.

The Act was first put into use in 1921 when the Triple Alliance (a predecessor of the TUC) was requested by the Miners' Federation of Great Britain to join a strike over a wage dispute.

[2] Also, during 1948 and 1949 there were lengthy unofficial strikes, particularly in the docks, so the Labour Attlee government implemented this Act to proclaim a state of emergency and used soldiers as strike-breakers by getting them to unload boats in London, Liverpool and Avonmouth.

In Episode 5 of Season 3 of The Crown, Lord Louis Mountbatten cites the 1920 Emergency Powers Act in the scene in which he meets with organizers of a possible coup d'état against the then Prime Minister, Harold Wilson.

On the occasion, he considers the Queen's powers and role vis-à-vis society, the Armed Forces and the legal system in a possible proclamation of national emergency to be central to the success of his plans.