Labour's electoral college chose Ed Miliband as the party's new leader on the basis of votes that were influenced by trade union activities. Some trade unions made a number of decisive interventions in the 2010 leadership election contest: they coordinated their nominations, canvassed intensely for their nominees (channelling considerable resources into their campaigns), and distributed ballots with strong recommendations in the same package as the voting slips. Such was the closeness of the election that, we argue, these interventions determined the result. This conclusion is all the more surprising since commentators and academics alike had maintained that the introduction of 'one member, one vote' had fundamentally reduced the role of trade unions in Labour party politics. In contrast, our opinion is that having been apparently deprived of control by the introduction of one member one vote, trade union elites developed a strategy to mould the outcome of the Labour leadership contest and so reassert their traditional influence over the party. Such was the extent of the role played by the trade unions that, we believe, the normative legitimacy of the electoral process by which Ed Miliband was elected can be called into question although the rules of the contest were not broken.