Heat a large frying pan until medium hot. Add the butter, shallot and curry powder and fry for 2-3 minutes, or until just softened.
Add the sweetcorn and all the liquid from the tin and then pour in the wine and enough water to just cover.
Bring to a simmer, add half of the cream and then season with salt and black pepper.
Bring the mixture back to the boil, remove from the heat to cool slightly and then transfer to a blender. Bend until smooth and return the soup to the pan to heat though.
Make some soured cream by whisking the remaining cream with the lemon juice until thickened.
Ladle the soup into a serving bowl and then top with a little of the crab, a spoonful of the soured cream and a drizzle of rapeseed oil.