Renowned social theorist Roberto Unger believes that left-of-centre progressives - his own political side - lack the imagination required to tackle the fundamental problems of society. In the run-up to the US presidential elections of 2012, he declared that his former student Barack Obama "must be defeated". Professor Unger argued that President Obama had failed in his first term in office to advance the progressive cause. There was, Unger maintained, effectively no difference between the Democrat and Republican political programmes.

In front of an audience at the London School of Economics and Political Science, Roberto Unger discusses with presenter Jo Fidgen the reasons for his critical appraisal of the progressive left in the United States and Europe. He sets out what he believes its alternative agenda should be and gives his verdict on another of his former students: Ed Miliband.

Roberto Mangabeira Unger is the Roscoe Pound professor at Harvard Law School. He served as a minister in the Brazilian government of President Luiz Inácio Lula da Silva from 2007-2009. His books include: "The Left Alternative"; "Democracy Realised"; and "The Self Awakened". His new book, published next year, will address a new theme: "The Religion of the Future".

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Producer: Simon Coates.