There was a certain amount of speculation at the IFG event about who would run for mayor of London in 2016.

BBC: The mayoral future for England's great cities

Mr Brown's I Feel Good (IFG) company, which publishes Hotdog and the official Leeds United monthly magazine, Leeds, Leeds, Leeds, was floated on the stock market last year.

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Lord Adonis, the IFG's boss and former Labour Transport Secretary, argued that London would not have had the Olympics, or Crossrail - the multi-billion rail tunnel through the heart of the city - or its congestion charge system, without an elected mayor.

BBC: The mayoral future for England's great cities