Sitting in a jerry-rigged boat, floating in a flooded sculpture park atop the Hayward as the sun bustles through the clouds and lights up the London Eye, the building's Brutalist architecture almost melts away and resolves itself into a dystopian reverie, one not entirely unpleasant: the capital has been lost, and the temples of culture abandoned to the damp elements. It's a daydream easy to believe in, until the wetsuit-wearing gallery aid comes and......