Despite widespread use the cognitive demands of the five-disc Tower of London (TOL) are unknown. Research suggests that conflict moves (those that are essential to the solution but do not place a disc in its final position) are a key aspect of performance. These were examined in three studies via a verification paradigm, in which normal participants were asked to decide whether a demonstrated move was correct. Experiment 1 showed that individual move latencies increase with the number of intermediate moves until the disc is placed in its goal position (resolution). Post hoc tests suggested that the number of alternative moves and moves to resolve a disc were independent predictors of performance. Experiment 2 successfully manipulated these factors in an experimental design. Experiment 3 showed that they remain determinants of performance as familiarity increased. Overall, errors on the task were significantly correlated with spatial memory. The implications of these findings for the use of the TOLin cognitive psychology and as an assessment tool are discussed.