No one could have missed the tin glittering in the hedge. It should have been an eyesore, another empty can cluttering the world   yet it seemed to me to belong with the lacy parsley layers, the cleaver stems clinging to nettle clumps and bony hawthorn branches,   with herb robert and long tickling grasses. Maybe the bright cylinder was a sculpture its maker thought would be stifled if displayed   on a gallery shelf so he bedded it outside in the succulence beneath an unshorn hedge. But it struck me as more than a work of art  …