Conscription was required in Britain during the First World War for several reasons.

Firstly, when the war broke out in 1914, the British government initially relied on voluntary enlistment to build up its army. However, as the war dragged on, it became clear that not enough men were coming forward to serve. By 1916, the number of volunteers had decreased significantly, and it was clear that Britain needed to take additional measures to increase the size of its army.

Secondly, the British army suffered heavy casualties during the first years of the war, particularly in the battles of the Somme and Passchendaele. These losses were not sustainable, and it was clear that Britain needed to recruit more men in order to continue fighting.

Thirdly, conscription was introduced as a response to the growing military power of Germany. Germany had introduced conscription before the war, and by 1916, it had a much larger army than Britain. In order to maintain a strong and competitive army, Britain needed to introduce conscription as well.

Overall, conscription was seen as a necessary measure to help win the war. The British government believed that by increasing the size of its army, it could better support its allies and push back against the enemy.

In Britain, conscription during the First World War was structured and operated through the Military Service Acts, which were passed by Parliament in 1916 and 1918.

Under the first Military Service Act of 1916, all unmarried men between the ages of 18 and 41 were required to register for military service, and were liable to be called up for service. Married men were not initially included in the conscription pool, but were added later that year. Men who were deemed medically unfit, or who were in certain essential occupations, such as farming or munitions production, could apply for exemptions from military service.

The second Military Service Act, passed in 1918, extended conscription to all men aged 18 to 50, and removed most exemptions. The only exceptions were for men who were medically unfit, those who had already served in the armed forces, and certain key workers who were deemed essential to the war effort.

Conscripts were typically assigned to the army, but some were also assigned to the navy or air force. Once called up for service, conscripts underwent basic training before being sent to the front lines or assigned to support roles.

There were some conscientious objectors who refused to serve in the military, citing religious or moral objections to war. These individuals were allowed to apply for exemption from military service, but if their application was denied, they faced imprisonment or other forms of punishment.

The introduction of conscription in Britain during the First World War was relatively smooth, with the majority of the population supporting the move. The British government initially relied on voluntary enlistment to build up its army, but as the war dragged on, it became clear that more men were needed to fight. In January 1916, the Military Service Act was passed, which introduced conscription for all unmarried men between the ages of 18 and 41. Married men were added to the conscription pool later that year.

There were some protests against conscription, particularly from pacifist groups and some trade unions, but these were relatively small and did not have a significant impact on the overall policy. Some conscientious objectors also refused to serve in the military, but they were offered alternative forms of service, such as working in non-combat roles or performing manual labor.

Overall, the introduction of conscription in Britain during the First World War was largely seen as a necessary measure to help win the war, and it did not lead to a significant crisis or widespread unrest.