Melt the butter in a large saucepan over medium heat.
Add the sliced leeks and cook gently for 5 minutes until softened.
Stir in the pumpkin and cook for another 2 minutes.
Pour in the vegetable stock and add the nutmeg.
Bring to a boil, then reduce the heat and simmer for 25 minutes.
Add the spinach and frozen peas, cooking for 5 minutes more.
Blend the soup until completely smooth.
Stir in the double cream and season with salt and black pepper.
Heat gently for 2 minutes without boiling.
Serve hot with fresh parsley for garnish.