Peel and dice cucumbers, place in saucepan with cold water, season with salt and bring to the boil. Drain well. Melt butter in large saucepan, add cucumbers, peeled and diced potatoes. Cover and simmer in own juices for 30 minutes. Sprinkle flour over cucumber/potatoes, stir well, and simmer for a minute. Add the milk, chicken stock and stir till thickened. Simmer 20 minutes. Season with salt, pepper, and sugar, add the extra butter and cream, plus the drained corn. Garnish with chopped chives/shallots.