In spring of 1939 the international situation was deteriorating and the British government under Neville Chamberlain was forced to consider prepartion of a war with Nazi Germany. In May 1939 this involved parliamentary approval being given for limited conscription applying to single men aged between 20 and 22. This required men to undertake six months' military training. About 240,000 men registered for service.
On the 3rd September 1939 Britain declared war on Germany, and on that day parliament immediately passed a more wide-reaching conscription measure. The National Service (Armed Forces) Act brought in conscription for all males aged between 18 and 41. These men had to register for service. Those who were medically unfit, and a number of workers in key industries, and those in jobs such as baking, farming, medicine and engineering were exempt.
In World War 2, provision was made for conscientious objectors. They had to appear before a tribunal to present their reasons for refusing to join up. If their cases were granted, they were categorised into several groups of exemption before they were given non-combatant jobs.
In order to further increase the number of people serving, in December 1941, a second National Service Act was passed. This brought in conscription for all unmarried women, and all childless widows between the ages of 20 and 30 liable for call-up.
At the same time, men were now required to do some form of National Service up to the age of 60, which included military service for those under 51. This allowed more men to be called up for police and civilian defence work, or for women to be called up for the auxiliary units of the armed forces.