Have British Trade Unions increased their power since the Second World War? To answer this question the concept of power is analysed. Three logically independent but contingently connected dimensions are distinguished: potential power, the exercise of power and the result of power. The bargaining power of a Trade Union is defined, independently of its potential power, as its exercise of power in institutionalized national wage rate bargaining with employers. A simplified model is devised, where bargaining power is operationalized in terms of preferences (claims) and the results of power (settlements). Application of this model to nine groups of workers represented by five large British Trade Unions shows that there has been no linear increa...