Britain is unusual among the combatant nations in that it still relies on volunteers to make up the numbers in its armed forces. Other countries conscripted men into their armies even in peacetime, but pressing men into military service seemed like an affront to the liberties of the British. This meant that Britain went into the war with a tiny army compared to those of its allies and enemies. Because of the terrible blood-letting since the start of the conflict, very few of the British soldiers who started the war are left in a fit shape to keep fighting it.
When the war started, the British authorities looked for volunteers to join the army and build it up in size. This appeal for new recruits has been very successful, with many young men joining up to do their bit for King and country. The army is now much larger than it was in August 1914, though its quality has gone down as the remaining professional troops have been diluted by the volunteers. Nevertheless, the authorities know that a continuous stream of recruits is necessary to keep the army up to strength. Although men are still volunteering in large numbers, the day may come when potential recruits decide that they would rather not expose themselves to the guns of the enemy.
And so steps are made towards introducing conscription. Today the National Registration Act becomes law. This does not provide for conscription but it lays the ground for it, by requiring men and women to register with the authorities. Once registered with the state bureaucracy it will be that bit easier for men to be forcibly inducted into the armed forces.
Lord Kitchener recruitment poster (Wikipedia)
Registration form (The Derby Scheme)