Swimming without a roof over your head has become a subversive activity, says Roger Deakin - and it's one he pursues with glee as he breast-strokes, crawls and occasionally paddles his way around some of the UK's more esoteric swimming places, from lazy ox-bow rivers to icy glacial lakes, from the balmy Scilly Islands to the Norfolk Broads. This is eccentricity elevated to an art form, a meditative hymn to the atavistic pleasures of water, which is expertly accentuated by Michael Kitchen's abrasively English reading. It's one to listen to again and again.