The British Socialist Party (BSP) opposed the war from the outset. The Independent Labour Party also maintained an anti-war policy from the start, even though some of its leading parliamentary members did not.
In addition, there was a considerable body of political opposition to the war which generated a host of anti-war organisations like the Union of Democratic Control and the No Conscription Fellowship. As the war progressed the lack of war aims coupled with the blundering of the military commanders, made it clear that the price of victory was to be paid through mass slaughter. Conscription was introduced in 1916.