Conscription during the First World War began when the British Government passed the Military Service Act  in 1916.

The act specified that single men aged 18 to 45 years old were liable to be called up for military service unless they were widowed with children or ministers of a religion.

There was a system of Military Service Tribunals to adjudicate upon claims for exemption on the grounds of performing civilian work of national importance, domestic hardship, health, and being a Conscientious Objector.

The law went through several changes before the war ended. Married men were exempt in the original Act, although this was changed in June 1916. The age limit was also eventually raised to 51 years old.

Recognition of work of national importance also diminished, and in the last year of the war there was some support for the conscription of clergy.

Conscription lasted until mid-1919.

More info: 

Call-up Paper for Alexander Thomson of Castle Street , Alloa
Call-up Paper for Alexander Thomson of Castle Street , Alloa.