Heat the oil in a large saucepan. Add the ginger, bacon, onion, carrot and celery and stir over a high heat for 1 minute. Add the leeks, reduce the heat to medium and cook for a further 4 minutes, stirring occasionally. Pour in the water and bring to the boil. Reduce the heat, cover the pan with a lid and simmer for 5 minutes.
Drain the crab, reserving the liquid, and set it aside. Stir the potatoes and reserved crab liquid into the soup. Bring back to simmering point, cover again and cook for about 10 minutes until the potatoes are tender.
Stir in the corn. Heat again to simmering point, then cover the pan and simmer for 5 minutes until the potatoes break up slightly and thicken the liquid. Lightly stir in the crab and dill (if using), cover the pan and remove it from the heat. Leave to stand for 5 minutes to allow the flavours to infuse. Season with freshly ground black pepper to taste.
Serve the chowder in warmed bowls topped with a spoonful of sour cream and a sprinkling of diced chilli, if you like.