The underclass is defined and the predictions are tested of three competing theories in the underclass debate. Using the National Child Development Study for the analysis it is found that an underclass suffering from a lack of qualifications, low cognitive ability and chronic joblessness exists. The validity of making a distinction between the working class and an underclass has often been questioned both because of the dubious history of such a distinction and because it is not believed that such a distinction is empirically true. The results contradict this assertion by finding the underclass to be distinctive from the working class in terms of patterns of family formation, work commitment and political allegiance. The distinct attitudes of the underclass, when coupled with evidence of inter- and intra-generational stability of membership, provide early evidence that a new social class, the underclass, may now exist in Britain.