Melt the butter in a pan until foaming, then add the leeks and fry for 4-5 minutes, or until tender.
Add the chopped potatoes, stock and wine to the pan and bring to boil. Reduce the heat to a simmer and cook for 20-25 minutes, or until the potatoes are tender.
Transfer the mixture to a food processor and blend until smooth. (Adjust the consistency of the soup, if needed, by adding water). Chill in the fridge for at least 30 minutes, or until completely cold.
Stir the cucumber into the soup, then add the lemon juice, to taste. Spoon the soup into serving bowls or glasses and swirl in the double cream. Sprinkle over the chopped chives and top each serving with a spoonful of crabmeat and a few slices of radish.
