For the fish stock, place all the fish stock ingredients into a large saucepan and pour over enough water to cover. Bring to the boil, then reduce the heat and simmer gently for ten minutes. Strain through a sieve and reserve the liquid.
For the soup, place all but two tablespoons of the peas into a saucepan with the butter and cook gently until the butter has melted and the peas have softened slightly.
Add the wine, turn up the heat and simmer until the liquid has reduced by half. Add the fish stock and simmer for 2-3 minutes. Remove from the heat and allow to cool slightly.
Pour the soup into a blender and blend until smooth. Return to the pan, add the remaining peas and the double cream and heat gently for 2-3 minutes.