Is a Turner painting long thought to be of a scene in Venice really a picture of Portsmouth? “If Turner expert Ian Warrell is right those dark shapes in the smoky gold light are not glamourous revellers, jaded with the pleasures of the most beautiful and decadent city in the world, being ferried home at dawn across the Venetian lagoon. They’re a bevy of Portsmouth councillors, local dignitaries, layabouts, rubberneckers and riffraff, setting out in a little Armada across the harbour to meet the King of France, Louis-Philippe.”