Remarkably, Billericay in Essex has one of the world's densest concentations of bluebells. For a few days each year, towards the end of April, or the beginning of May, between the warming of the soil and the closing of the leaof canopy, millions of bluebells bloom here. The brevity of the bloom gives the sense of the circus coming to town for a few days only. Transience is everywhere at play: in the way that the light falls and changes the colour of the woodland floor. When the sun's high at noon, there's a saphire dazzle that leaves an imprint on your retina when you look away. The poet Gerald Manley Hopkins was fascinated by bluebells. He wrote of the "blue-buzzed haze" and how "woodland banks wash wet like lakes" lines that make instant sense when you visit a bluebell woodland like this one.