The Bill which became the Act was introduced by Prime Minister H.H. Asquith in January 1916. It came into force on 02 March 1916. Previously the British Government had relied on voluntary enlistment, and latterly a kind of moral conscription called the Derby Scheme.
The conscription issue divided the Liberal Party including the Cabinet. Sir John Simon resigned as Home Secretary and attacked the government in his resignation speech in the House of Commons, where 35 Liberals voted against the bill, alongside 13 Labour MPs and 59 Irish Nationalists.
The Act specified that men from 18 to 41 years old were liable to be called up for service in the army unless they were eligible for exemptions listed under this Act, including men who were married, widowed with children, serving in the Royal Navy, a minister of religion, or working in one of a number of reserved occupations, or for conscientious objection. A second Act in May 1916 extended liability for military service to married men, and a third Act in 1918 extended the upper age limit to 51.
Men or employers who objected to an individual’s call-up could apply to a local Military Service Tribunal. These tribunals had powers to grant exemption from service, usually conditional or temporary, under the eligibility criteria which for the first time in history included conscientious objection. There was right of appeal to a County Appeal Tribunal, and finally to a Central Tribunal in Westminster in London.
Due to political considerations, after the Easter Rising, the Act did not extend to Ireland, which was then part of the United Kingdom. The Conscription Crisis of 1918 occurred when the British Government tried to impose conscription on Ireland, leading to increased support for Sinn Féin. The government and the Irish media had wrongly blamed Sinn Féin, then a small monarchist political party with little popular support for the rebellion, even though it had not been involved.