In the spring of 1915 voluntary enlistments had averaged 100,000 men per month, but this was unsustainable. The upper age limit was raised but it became clear that voluntary recruitment was insufficient
On 15th July 1915 the government passed the National Registration Act to stimulate recruitment and to discover how many men aged between 15 and 65 were engaged in each trade. The results of this census showed there were nearly 5 million males of military age who were not in the forces, if which 1.6 million were in the protected, high or scarce skills jobs.
Edward Stanley, Lord Derby played a major part in raising volunteers and was appointed Director-General of Recruiting in October 1915. Within 5 days of his appointment he brought forward a programme, often called the Derby Scheme although its official title was the Group Scheme, for raising the numbers. The scheme informed men aged 18 to 40 that they could continue to enlist voluntarily or attest with an obligation to come if called up later on.
The War Office notified the public that the last day for voluntary enlistment would be 15 December 1915.