Left-Revolutionary Communism, Right-Revolutionary Socialism. This is where the labeling of Nazi Socialism as right wing" comes from.

Thus when the socialist movement returned to Britain in the 1880s there were two more or less clearly defined trends within Socialism—a right and a left: a reformist trend, which talked about the advance to Socialism in terms of social reform, as something gradual, piecemeal, peaceful, within the framework of capitalism; and a Marxist revolutionary trend, which understood the class struggle and saw that Socialism could be achieved only if the working people, led by the working class, won political power.

In this period, 1880-1914, the working class again began to develop the struggle to form their own independent political parties. The MarxistSocial Democratic Federation was formed in 1883, and the Socialist League led by William Morris, in 1884. The Independent Labour Party was founded in 1893, and the Labour Party (at first the Labour Representation Committee) in 1900. Why was it that these political parties and groupings were not adequate to lead the British people to the victory of Socialism?

In essence this was the position. The trade unions were great mass organisations, the greatest in the world. But the role of the unions was to defend and improve the living conditions of the workers; they were not socialist bodies. Vital though they were, they could not lead the political struggle for the defeat of the capitalist system.

http://www.marxists.org/history/international/comintern/sections/britain/partyed/1955/rolecom.htm