Political knowledge has been shown to influence a host of substantively important outcomes, such as participation, issue preference and vote choice. The causes of individual heterogeneity in knowledge have gone relatively unexplored however. What leads some individuals to become political sophisticates and others not? Generally, motivation has been considered as key in this regard; those who are interested in politics seek out and retain political information which leads, in turn, to higher levels of interest in politics. Using data from the 1992-1997 and 1997-2001 British Election Panel Studies, however, we find no evidence of a reciprocal effects mechanism. Although this ‘virtuous circle’ model of sophistication has accrued some empirical support in the US, with British data we find evidence only for a uni-directional effect from interest to knowledge. We argue that previous analyses are potentially flawed due to their reliance on cross-sectional data and likely violation of model assumptions.